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SPM Additional Science study materials
SPM Additional Science study resources

SPM Additional Science practice questions

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Question 1Scientific Skills and Investigation

A student records the length of a metal rod as 12.45 cm using a ruler whose smallest division is 0.1 cm. Which statement about this reading is correct?

  1. The reading is invalid because a ruler cannot measure to 0.01 cm.
  2. The reading should be rounded to 12 cm because rulers are imprecise.
  3. The reading must be repeated exactly to confirm the estimated digit.
  4. The reading contains an estimated digit and is acceptable for a ruler with 0.1 cm divisions. Correct answer.

Explanation

When using an analogue scale, the last recorded digit is an estimate between the smallest divisions, so a ruler marked in 0.1 cm can reasonably be read to 0.01 cm. The value 12.45 cm therefore contains one estimated digit and is acceptable.

Question 2Scientific Skills and Investigation

In an experiment, the manipulated variable is the concentration of hydrochloric acid and the responding variable is the time taken for magnesium ribbon to dissolve. Which variable must be kept constant to make the comparison fair?

  1. The time taken for the ribbon to dissolve
  2. The concentration of the acid
  3. The volume of acid used Correct answer.
  4. The rate of gas production

Explanation

A fair test changes only the manipulated variable, so all other relevant conditions must be controlled. The volume of acid affects the amount of reactant available and must be fixed. Time and concentration are already the responding and manipulated variables.

Question 3Scientific Skills and Investigation

A student measures the mass of a sample three times and obtains 4.82 g, 4.85 g and 4.83 g, while the accepted value is 5.20 g. Which description of the measurements is correct?

  1. They are precise but not accurate. Correct answer.
  2. They are both accurate and precise.
  3. They are neither precise nor accurate.
  4. They are accurate but not precise.

Explanation

Precision refers to how closely repeated readings agree with each other, while accuracy refers to closeness to the true value. The three readings cluster tightly together but all lie far below 5.20 g, so they are precise but inaccurate.

Question 4Scientific Skills and Investigation

Which instrument is most suitable for measuring 25.0 cm³ of a solution to be used in a titration where high accuracy is required?

  1. A 25 cm³ pipette Correct answer.
  2. A 100 cm³ beaker
  3. A 10 cm³ syringe
  4. A 50 cm³ measuring cylinder

Explanation

A pipette delivers a single fixed volume with high accuracy, making it the standard choice for transferring a precise aliquot in a titration. Measuring cylinders and beakers have coarser graduations and larger uncertainty.

Question 5Scientific Skills and Investigation

A table of results lists the independent variable in the left column and the dependent variable in the right column. Which additional feature is essential for a well-constructed results table?

  1. A sketch of the apparatus above the table
  2. A conclusion paragraph below the table
  3. Units stated in the column headings Correct answer.
  4. The name of the student in each row

Explanation

Every column of numerical data must state the quantity and its unit in the heading so the values are unambiguous. Apparatus sketches and conclusions belong elsewhere in a report, not inside the data table itself.

Question 6Scientific Skills and Investigation

Which statement best describes a hypothesis in a scientific investigation?

  1. A testable proposed explanation that can be supported or rejected by evidence Correct answer.
  2. A list of apparatus required for the experiment
  3. A final conclusion drawn after all data have been analysed
  4. A description of the steps followed during the experiment

Explanation

A hypothesis is a tentative, testable statement that predicts a relationship between variables and can be checked against experimental evidence. It is made before data collection and may be supported or rejected.

Question 7Scientific Skills and Investigation

A student plots a graph of extension against load and obtains a straight line passing through the origin. What does the gradient of this line represent?

  1. The stiffness of the spring Correct answer.
  2. The mass of the load
  3. The elastic limit of the spring
  4. The total length of the spring

Explanation

For a straight-line graph through the origin, the gradient equals the change in the y-variable per unit change in the x-variable. Here that is extension per unit load, which measures the spring's stiffness (the reciprocal of the spring constant).

Question 8Scientific Skills and Investigation

The following measurements of a quantity are recorded: 2.4 s, 2.6 s, 2.5 s, 2.5 s, 6.8 s. Which action is most appropriate before calculating the mean?

  1. Use only the highest and lowest values
  2. Discard 6.8 s as an anomalous result after checking for a recording error Correct answer.
  3. Include all values because every reading is data
  4. Round all values to 3 s and then average

Explanation

A value that lies far from the cluster of other readings is likely anomalous and should be checked for experimental or recording error before being excluded from the mean. Including it would distort the average and misrepresent the data.

Question 9Scientific Skills and Investigation

A student wants to investigate how the rate of photosynthesis in pondweed changes with light intensity. Which combination of variables is correctly identified?

  1. Manipulated: temperature; responding: light intensity; controlled: number of bubbles
  2. Manipulated: number of bubbles; responding: light intensity; controlled: temperature
  3. Manipulated: light intensity; responding: number of bubbles per minute; controlled: temperature Correct answer.
  4. Manipulated: light intensity; responding: temperature; controlled: number of bubbles

Explanation

The variable deliberately changed is light intensity, and the outcome measured is the bubble count per minute, which indicates the rate of photosynthesis. Temperature must be kept constant because it also affects enzyme activity.

Question 10Scientific Skills and Investigation

Which statement correctly distinguishes a systematic error from a random error?

  1. Both types of error can be eliminated by taking more readings.
  2. A systematic error shifts all readings in the same direction, while a random error scatters readings about a mean. Correct answer.
  3. A systematic error scatters readings, while a random error shifts all readings equally.
  4. A systematic error only affects the largest reading in a set.

Explanation

Systematic errors arise from a consistent fault such as a zero error and bias every reading by a similar amount. Random errors vary unpredictably and tend to average out when many readings are taken.

Question 11Scientific Skills and Investigation

A student uses a stopwatch to time 20 oscillations of a pendulum and divides the total time by 20. Why is this method preferred to timing a single oscillation?

  1. It reduces the effect of human reaction time on the result Correct answer.
  2. It makes the pendulum swing faster
  3. It changes the period of the pendulum
  4. It removes all systematic errors from the stopwatch

Explanation

Human reaction time introduces a roughly fixed uncertainty at the start and stop of timing. Timing many oscillations and dividing spreads that uncertainty over a longer interval, reducing its relative effect on the period.

Question 12Scientific Skills and Investigation

In a report, a student writes: 'The higher the temperature, the faster the tablet dissolves.' Which type of statement is this?

  1. A controlled variable
  2. A conclusion supported by collected data
  3. A measurement with units
  4. A hypothesis linking two variables Correct answer.

Explanation

The statement proposes a testable relationship between temperature and dissolving time before data are presented, which is the role of a hypothesis. A conclusion would require evidence from the results.

Question 13Scientific Skills and Investigation

A graph of volume against temperature for a gas gives a straight line that does not pass through the origin. What is the most appropriate interpretation?

  1. There is a systematic offset, such as a zero error or an excluded constant Correct answer.
  2. The data are invalid and must be discarded
  3. The gas does not obey any relationship with temperature
  4. Volume is the manipulated variable

Explanation

A straight line indicates a linear relationship, but an intercept displaced from the origin suggests a constant offset. This may arise from a zero error in the apparatus or from a physical constant in the relationship that shifts the line.

Question 14Scientific Skills and Investigation

A student measures the diameter of a wire with a micrometer screw gauge and obtains 0.48 mm, 0.49 mm and 0.48 mm. The instrument has a zero error of +0.02 mm. What is the corrected mean diameter?

  1. 0.48 mm
  2. 0.50 mm
  3. 0.51 mm
  4. 0.46 mm Correct answer.

Explanation

The mean of the readings is 0.483 mm, approximately 0.48 mm. A positive zero error means the instrument reads too high, so the error must be subtracted: 0.48 - 0.02 = 0.46 mm.

Question 15Scientific Skills and Investigation

A student claims that increasing the concentration of acid always increases the rate of reaction. Which observation would most directly challenge this claim?

  1. A higher concentration producing more gas bubbles per minute
  2. A higher concentration producing the same rate once the metal surface is fully covered Correct answer.
  3. A lower concentration producing fewer bubbles per minute
  4. A change in temperature during the reaction

Explanation

A claim of 'always' is challenged by any case where the expected effect fails to appear. If the rate stops increasing because the surface is saturated, the simple relationship breaks down, refuting the absolute claim.

Question 16Scientific Skills and Investigation

Which feature of a line graph allows a student to determine whether two variables are directly proportional?

  1. A curve that rises steeply
  2. A line with a negative gradient
  3. A line that crosses the vertical axis above the origin
  4. A straight line passing through the origin Correct answer.

Explanation

Direct proportionality requires that one variable be a constant multiple of the other, which graphs as a straight line through the origin. A curve, a negative gradient, or a non-zero intercept shows a different relationship.

Question 17Scientific Skills and Investigation

A student wants to reduce the percentage uncertainty in a measurement of the time for a reaction to complete. Which strategy is most effective?

  1. Recording only one reading instead of several
  2. Rounding the time to the nearest whole second
  3. Measuring a longer reaction time under otherwise similar conditions Correct answer.
  4. Using a stopwatch with a coarser scale

Explanation

Percentage uncertainty is the absolute uncertainty divided by the measured value, so a larger measured value reduces the percentage uncertainty. Measuring a longer time therefore lowers the relative effect of reaction-time error.

Question 18Scientific Skills and Investigation

An experiment produces the following pairs of values: (1, 2.0), (2, 4.1), (3, 5.9), (4, 8.2), (5, 10.1). A student concludes the relationship is y = 2x. Which statement best evaluates this conclusion?

  1. It is rejected because the values are not exactly double
  2. It is invalid because the data contain too many points
  3. It is fully supported because every y value is close to twice x
  4. It is approximately supported, but the small deviations suggest random error rather than an exact law Correct answer.

Explanation

Each y value lies close to 2x, so the relationship is approximately linear and proportional. Small deviations are expected from random measurement error, so the data support but do not prove an exact law.

Question 19Scientific Skills and Investigation

A student measures the mass of a crucible before and after heating a hydrate, then calculates the mass of water lost by subtraction. Which source of error would have the greatest relative effect on the calculated mass of water?

  1. A constant zero error in the balance
  2. A small random fluctuation in the balance readings Correct answer.
  3. Using a balance with a readability of 0.01 g
  4. Heating the crucible for slightly longer than needed

Explanation

The mass of water is found by subtracting two similar balance readings, so the result is small compared with each reading. Random fluctuations of fixed absolute size therefore become a large fraction of the calculated difference, giving the greatest relative effect.

Question 20Scientific Skills and Investigation

Two students investigate the same reaction. Student A uses a measuring cylinder and Student B uses a burette. Their mean results differ by 0.3 cm³, and each student's repeated readings vary by only 0.05 cm³. Which interpretation is most defensible?

  1. The difference is likely systematic, arising from the different apparatus used Correct answer.
  2. The difference is due to random error because repeats vary little
  3. The difference is too small to matter in any investigation
  4. The difference proves that Student A's readings are invalid

Explanation

Small variation among repeats shows that random error is low, so a consistent difference between two students points to a systematic cause. Using different apparatus with different graduations is a plausible source of such a bias.

Question 21Matter and Atomic Structure

Which particle in an atom carries a negative charge and orbits the nucleus?

  1. Nucleon
  2. Electron Correct answer.
  3. Neutron
  4. Proton

Explanation

Electrons are negatively charged particles found in shells around the nucleus. Protons are positive and neutrons are neutral, so neither carries a negative charge. The term nucleon refers collectively to protons and neutrons, not to a negatively charged particle.

Question 22Matter and Atomic Structure

An atom of an element has proton number 11 and nucleon number 23. How many neutrons does it contain?

  1. 34
  2. 12 Correct answer.
  3. 11
  4. 23

Explanation

The number of neutrons equals the nucleon number minus the proton number, that is 23 − 11 = 12. The proton number gives protons only, and the nucleon number is the total of protons plus neutrons. Adding the two numbers would wrongly count protons twice.

Question 23Matter and Atomic Structure

Which statement describes isotopes of an element?

  1. Atoms with the same number of protons but different numbers of neutrons Correct answer.
  2. Atoms with the same number of electrons but different numbers of protons
  3. Atoms with the same nucleon number but different proton numbers
  4. Atoms with the same number of neutrons but different numbers of protons

Explanation

Isotopes are atoms of the same element, so they share the same proton number, but they differ in neutron number and therefore in nucleon number. Having different proton numbers would make them different elements entirely. Identical nucleon number with different proton number is not the definition of isotopes.

Question 24Matter and Atomic Structure

Which arrangement lists the particles of an atom in order of increasing mass?

  1. Neutron, electron, proton
  2. Electron, proton, neutron Correct answer.
  3. Electron, neutron, proton
  4. Proton, electron, neutron

Explanation

The electron has a mass of about 1/1840 of a proton, so it is by far the lightest. The proton and neutron have almost equal masses, with the neutron slightly heavier. Hence the order electron, proton, neutron is the correct increasing sequence.

Question 25Matter and Atomic Structure

In the modern periodic table, elements are arranged in order of increasing

  1. number of neutrons
  2. proton number Correct answer.
  3. nucleon number
  4. relative atomic mass

Explanation

The modern periodic table orders elements by increasing proton number, which is the basis of periodicity. Mendeleev originally used relative atomic mass, but this was later replaced because it placed some elements wrongly. Nucleon number and neutron number vary among isotopes and do not give a consistent order.

Question 26Matter and Atomic Structure

Which group of the periodic table contains the noble gases?

  1. Group 18 Correct answer.
  2. Group 17
  3. Group 2
  4. Group 1

Explanation

The noble gases occupy Group 18, the rightmost column of the periodic table, and have full outer electron shells. Group 1 holds the alkali metals and Group 2 the alkaline earth metals. Group 17 contains the halogens, which are reactive non-metals.

Question 27Matter and Atomic Structure

An element in Group 1 forms a positive ion. What happens to its atom when the ion forms?

  1. It loses one electron from its outer shell Correct answer.
  2. It gains one electron into its outer shell
  3. It gains one neutron into its nucleus
  4. It loses one proton from its nucleus

Explanation

Group 1 atoms have a single outer electron, which they lose to achieve a stable noble-gas configuration, forming a 1+ ion. Losing a proton would change the element itself, which does not happen in ordinary ion formation. Neutrons are not gained or lost during ion formation.

Question 28Matter and Atomic Structure

Chlorine exists as two isotopes, chlorine-35 and chlorine-37, in roughly a 3:1 ratio. What is the approximate relative atomic mass of chlorine?

  1. 37.0
  2. 36.0
  3. 36.5
  4. 35.5 Correct answer.

Explanation

The relative atomic mass is the weighted average of isotope masses by abundance: (35 × 3 + 37 × 1) ÷ 4 = 35.5. A simple average of 36 ignores the greater abundance of chlorine-35. Values of 36.5 or 37 would require a much larger proportion of the heavier isotope.

Question 29Matter and Atomic Structure

Which pair of atoms are isotopes of the same element?

  1. Atom with 8 protons and 8 neutrons; atom with 8 protons and 10 neutrons Correct answer.
  2. Atom with 8 protons and 8 neutrons; atom with 8 protons and 9 electrons
  3. Atom with 8 protons and 8 neutrons; atom with 9 protons and 8 neutrons
  4. Atom with 8 protons and 8 neutrons; atom with 9 protons and 10 neutrons

Explanation

Isotopes must have the same proton number but different neutron numbers. The first pair both have 8 protons but differ in neutrons (8 and 10), so they are isotopes of the same element. Pairs with different proton numbers are different elements, and a difference in electrons alone describes an ion, not an isotope.

Question 30Matter and Atomic Structure

Across Period 3 from sodium to chlorine, which trend is observed?

  1. All elements remain strongly non-metallic
  2. The elements change from metallic to non-metallic character Correct answer.
  3. The elements change from non-metallic to metallic character
  4. All elements remain strongly metallic

Explanation

Across a period the proton number increases while electrons enter the same shell, so the nucleus attracts outer electrons more strongly and metallic character decreases. Sodium at the start is a reactive metal, while chlorine near the end is a reactive non-metal. The opposite trend, non-metal to metal, occurs down a group rather than across a period.

Question 31Matter and Atomic Structure

Why do elements in the same group of the periodic table show similar chemical properties?

  1. They have identical numbers of neutrons
  2. They have the same number of electron shells
  3. They have identical nucleon numbers
  4. They have the same number of electrons in their outer shell Correct answer.

Explanation

Chemical properties are governed mainly by the outer-shell electrons, and elements in a group share the same outer-shell configuration. The number of shells increases down a group, so that cannot explain similarity. Nucleon and neutron numbers vary between elements and are not the basis of group similarity.

Question 32Matter and Atomic Structure

An atom of an element has the electronic configuration 2.8.7. In which group and period is it placed?

  1. Group 7, Period 3
  2. Group 15, Period 2
  3. Group 3, Period 17
  4. Group 17, Period 3 Correct answer.

Explanation

The configuration 2.8.7 has three occupied shells, so the element is in Period 3. It has seven outer electrons, placing it in Group 17, the halogens. Writing the group as 7 is a common error because the outer-shell count is 7, but the group number is 17.

Question 33Matter and Atomic Structure

When a magnesium atom forms its ion, it loses two electrons. What is the charge of the resulting ion?

  1. 2+ Correct answer.
  2. 2−
  3. 1+
  4. 0

Explanation

Losing two electrons removes two negative charges, leaving two more protons than electrons, so the ion has a charge of 2+. Gaining electrons would give a negative charge, but magnesium loses them. A charge of 0 would mean equal protons and electrons, which is the neutral atom.

Question 34Matter and Atomic Structure

Which statement about the nucleus of an atom is correct?

  1. It contains only protons and carries no charge
  2. It contains protons and electrons and holds nearly all the atom's mass
  3. It contains protons and neutrons and holds nearly all the atom's mass Correct answer.
  4. It contains neutrons and electrons and carries a positive charge

Explanation

The nucleus contains protons and neutrons, whose combined mass accounts for almost the entire mass of the atom. Electrons are outside the nucleus and contribute negligible mass. Because of the protons, the nucleus carries a positive charge, not a neutral one.

Question 35Matter and Atomic Structure

A neutral atom has 16 protons, 16 neutrons and 16 electrons. Which description of this atom is correct?

  1. Proton number 32, nucleon number 16
  2. Proton number 16, nucleon number 32 Correct answer.
  3. Proton number 16, nucleon number 16
  4. Proton number 32, nucleon number 32

Explanation

The proton number equals the number of protons, which is 16. The nucleon number is the sum of protons and neutrons, 16 + 16 = 32. Electrons are not counted in the nucleon number, and the proton number is never the sum of protons and neutrons.

Question 36Matter and Atomic Structure

Which statement best explains why the relative atomic mass of an element is often not a whole number?

  1. It counts only the heaviest isotope present in the sample
  2. It equals the number of protons plus the number of electrons
  3. It is a weighted average of the masses of its naturally occurring isotopes Correct answer.
  4. It is the average mass of the element's ions

Explanation

Most elements exist as a mixture of isotopes with different masses, so the relative atomic mass is the abundance-weighted average of these masses. Because the proportions are usually not simple whole-number ratios, the average is often fractional. Counting only the heaviest isotope or averaging ions would not give the accepted value.

Question 37Matter and Atomic Structure

Element X has proton number 17. Element Y has proton number 18. Which comparison of these two neutral atoms is correct?

  1. X and Y have the same number of outer electrons and similar reactivity
  2. Y has one more outer electron than X and is more reactive
  3. X has one more outer electron than Y and is more reactive Correct answer.
  4. X has one fewer electron shell than Y and is less reactive

Explanation

Element X with proton number 17 has the configuration 2.8.7, while Y with 18 has 2.8.8. Thus X has one more outer electron, and because it needs only one more to complete its shell it is a reactive halogen. Y has a full outer shell, making it an unreactive noble gas.

Question 38Matter and Atomic Structure

A sample of an element consists of 75% of isotope A (mass 10) and 25% of isotope B (mass 11). What is the relative atomic mass of the element?

  1. 11.00
  2. 10.50
  3. 10.25 Correct answer.
  4. 10.75

Explanation

The weighted average is (10 × 0.75) + (11 × 0.25) = 7.5 + 2.75 = 10.25. A value of 10.50 would result from an equal 50:50 mixture, which is not given. Values closer to 11 would require isotope B to be much more abundant than 25%.

Question 39Matter and Atomic Structure

An ion has 13 protons, 14 neutrons and 10 electrons. Which identification of this ion is correct?

  1. An aluminium ion with charge 3−
  2. An aluminium ion with charge 3+ Correct answer.
  3. A silicon ion with charge 3+
  4. A neon ion with charge 3−

Explanation

The element is set by the proton number 13, which is aluminium. With 13 protons and only 10 electrons, there are three more positive charges than negative, so the ion has a charge of 3+. A charge of 3− would require more electrons than protons, and silicon or neon would need different proton numbers.

Question 40Matter and Atomic Structure

Why does the first ionisation energy generally increase across a period from left to right?

  1. The atomic radius increases, so less energy is needed to remove the outer electron
  2. The number of electron shells increases, so the outer electron is farther from the nucleus
  3. The number of neutrons increases, so the nucleus attracts electrons more strongly
  4. The proton number increases while electrons enter the same shell, so the outer electron is held more strongly Correct answer.

Explanation

Across a period the nuclear charge rises while the outer electrons stay in the same shell, so the effective attraction on the outer electron increases and more energy is needed to remove it. An increasing number of shells occurs down a group, where ionisation energy generally falls. Neutron number does not govern the attraction on electrons.

Question 41Chemical Reactions and Equations

Which observation shows that a chemical reaction has taken place when dilute hydrochloric acid is added to zinc granules?

  1. The total mass of the mixture increases during the reaction
  2. The acid becomes a paler yellow colour
  3. Bubbles of gas are released and the mixture warms up Correct answer.
  4. The zinc granules settle at the bottom of the test tube

Explanation

A chemical reaction is shown by the formation of a new substance, here hydrogen gas, together with a temperature change as bonds are broken and formed. Colour change, gas evolution and heat change are all accepted signs of reaction, but only the bubbling and warming fit the zinc-acid reaction.

Question 42Chemical Reactions and Equations

In the equation 2Mg + O2 -> 2MgO, what does the coefficient 2 in front of MgO tell you?

  1. The molar mass of magnesium oxide is doubled
  2. Two atoms of oxygen are present in each magnesium oxide unit
  3. The magnesium oxide produced has twice the mass of the magnesium
  4. Two moles of magnesium oxide are produced for every mole of oxygen used Correct answer.

Explanation

A coefficient in a balanced equation gives the mole ratio in which substances react and are produced. Here one mole of O2 reacts with two moles of Mg to give two moles of MgO, so the coefficient is a stoichiometric ratio, not a mass or formula detail.

Question 43Chemical Reactions and Equations

Which of the following is a correct balanced equation for the complete combustion of methane?

  1. CH4 + 2O2 -> CO2 + 2H2O Correct answer.
  2. CH4 + 3O2 -> CO2 + 2H2O
  3. 2CH4 + O2 -> 2CO2 + H2O
  4. CH4 + O2 -> CO2 + H2O

Explanation

Balancing requires equal numbers of each atom on both sides. CH4 + 2O2 gives one carbon, four hydrogen and four oxygen atoms on each side, so the equation is balanced.

Question 44Chemical Reactions and Equations

Which statement best describes a mole of a substance?

  1. The volume occupied by one gram of the substance
  2. The amount containing 6.02 x 10^23 particles of that substance Correct answer.
  3. The number of atoms in one gram of the substance
  4. The mass of one molecule of the substance in grams

Explanation

The mole is the amount of substance containing the Avogadro number, about 6.02 x 10^23, of particles. It links the particle scale to measurable masses through the molar mass.

Question 45Chemical Reactions and Equations

Which type of reaction is represented by AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)?

  1. Thermal decomposition
  2. Precipitation Correct answer.
  3. Combustion
  4. Neutralisation

Explanation

An insoluble solid, silver chloride, forms when two solutions are mixed, which is the defining feature of a precipitation reaction. The ions exchange partners but no acid-base neutralisation or combustion occurs.

Question 46Chemical Reactions and Equations

Which ion is responsible for the acidic properties of an aqueous solution?

  1. Hydroxide ion, OH-
  2. Chloride ion, Cl-
  3. Sodium ion, Na+
  4. Hydrogen ion, H+ Correct answer.

Explanation

Acids release hydrogen ions, H+, in water, and this ion is responsible for acidity. Hydroxide ions cause alkalinity, while chloride and sodium ions are spectator ions in many acid reactions.

Question 47Chemical Reactions and Equations

Which property is characteristic of an ionic compound such as sodium chloride?

  1. It conducts electricity when molten but not when solid Correct answer.
  2. It conducts electricity in the solid state
  3. It has a low melting point and is a gas at room temperature
  4. It exists as simple molecules with weak forces between them

Explanation

Ionic compounds form a lattice of ions held by strong electrostatic forces, so they are solid at room temperature and do not conduct when the ions are fixed. When molten, the ions become mobile and can carry charge, so conduction occurs.

Question 48Chemical Reactions and Equations

A student adds magnesium ribbon to excess dilute sulfuric acid and measures the volume of gas collected over time. Which change increases the initial rate of reaction?

  1. Using a larger conical flask
  2. Cooling the reaction mixture in an ice bath
  3. Diluting the acid with an equal volume of water
  4. Using powdered magnesium instead of ribbon Correct answer.

Explanation

Rate depends on the frequency of successful collisions between particles. Powdered magnesium has a larger surface area, so more acid particles can collide with the metal each second and the initial rate rises.

Question 49Chemical Reactions and Equations

In the reaction CuO + H2 -> Cu + H2O, which substance is oxidised?

  1. Copper
  2. Hydrogen Correct answer.
  3. Water
  4. Copper(II) oxide

Explanation

Oxidation can be defined as loss of electrons or gain of oxygen. Hydrogen gains oxygen to form water, so it is oxidised, while copper(II) oxide loses oxygen and is reduced.

Question 50Chemical Reactions and Equations

What is the mass of 0.25 mol of calcium carbonate, CaCO3? (Ar: Ca=40, C=12, O=16)

  1. 25 g Correct answer.
  2. 100 g
  3. 10 g
  4. 50 g

Explanation

The molar mass of CaCO3 is 40 + 12 + 48 = 100 g/mol. Mass equals moles multiplied by molar mass, so 0.25 x 100 = 25 g.