Conservation of mass & balanced equations

A student investigates the reaction that occurs when zinc carbonate is heated.

Figure 1 shows the apparatus the student uses.

What is the name of the piece of apparatus labelled G in Figure 1?

State what apparatus should be used to heat the zinc carbonate in Figure 1.

The word equation for the reaction that occurs when zinc carbonate is heated is

zinc carbonate zinc oxide + carbon dioxide

The carbon dioxide bubbles through the limewater.

State what is seen when carbon dioxide bubbles through the limewater.

Another student investigates the change in mass that takes place when zinc carbonate is heated.

Figure 2 shows the results the student records at the start of the investigation.

Using the results in Figure 2, calculate the mass of zinc carbonate in the test tube.

mass of zinc carbonate =_........ g

The student then

• heats the test tube containing the zinc carbonate for five minutes

• places the hot test tube on a bench mat to cool

• finds the mass of the test tube and contents.

Describe what the student should do next to make sure that all the zinc carbonate has reacted completely.

This question is about metals and their reactions with acids.

Place ticks () in boxes to show which elements in the table are metals.

Use the periodic table to help you answer this question.

Three equal sized pieces of the metals E, F, G and H are put into separate test tubes containing equal volumes of dilute sulfuric acid.

The results in Figure 6 show the test tubes after half a minute.

Arrange the metals E, F, G and H in order of reactivity.

The bubbles that form are hydrogen.

Which row of the table shows the test and result that confirm the gas is hydrogen?

When zinc reacts with very dilute nitric acid, zinc nitrate is formed.

The formula of zinc nitrate is Zn(NO₃)₂

Calculate the relative formula mass of zinc nitrate, Zn(NO₃)₂

(relative atomic masses: Zn = 65, N = 14, O = 16)

relative formula mass =_........

A student investigates the reaction between a metal and a dilute acid using the apparatus shown in Figure 7.

Cotton wool is placed in the top of the apparatus as shown, to stop any acid from spraying out.

The total mass of the apparatus is shown at the start of the reaction and after the reaction has ended.

start of reaction end of reaction

Figure 7

State two ways the student would know that the reaction has ended.

This question is about gases.

When sodium is added to water, hydrogen gas is produced.

Which observation shows that a gas has been produced?

Some damp litmus paper is placed in a gas. The litmus paper is bleached.

Which gas bleaches damp litmus paper?

When calcium carbonate is heated it decomposes.

When 5.000 g of calcium carbonate is heated, the mass of solid remaining is 2.800 g.

Calculate the mass of carbon dioxide that has been released.

Give your answer to three significant figures.

mass of carbon dioxide =_........ g

A diagram of an atom of helium is shown in Figure 9.

Explain, using Figure 9, why helium is inert.

Helium is used to fill balloons.

State one property of helium, apart from it being inert, that makes it suitable for filling balloons.

*(e) Figure 10 shows the relative amounts of three gases in the early atmosphere compared to the composition of today’s atmosphere.

Natural processes and human activities have altered the relative amounts of these gases in the atmosphere.

Explain how the relative amount of each of the gases in Figure 10 has increased or decreased over time.

A student investigated the reaction between potassium iodide and lead nitrate.

Solutions of potassium iodide and lead nitrate were mixed together. Lead iodide and potassium nitrate were formed.

Complete the word equation.

The student recorded the total mass of the reactants and the total mass of the products.

The results are shown in Figure 2.

State how the results in Figure 2 show that mass is conserved in this reaction.

In another experiment, a student investigated the temperature decrease when different amounts of ammonium nitrate crystals were dissolved in 100 cm³ of water.

The apparatus used is shown in Figure 3.

The student used the following method.

step N $pour 100 cm³ of water into the polystyrene cup

step 2 add one spatula of ammonium nitrate crystals to the water

step 3 stir the mixture

step 4 use the thermometer to record the lowest temperature reached by the mixtur e

step 5 repeat steps 1 to 4 using different amounts of ammonium nitrate

Name a piece of apparatus that should be used to measure the 100 cm³ of water in step 1.

The student cannot work out the temperature decrease using the method described.

State what the student must do before step 2 to be able to work out the temperature decrease.

State why a polystyrene cup is used in this experiment.

Figure 4 shows the reaction profile for this reaction.

Use the words from the box to complete the labels on Figure 4.

The word equation for the reaction between magnesium and dilute hydrochloric acid is

magnesium + hydrochloric acid magnesium chloride + hydrogen

The reaction was carried out using the apparatus shown in Figure 6.

A strip of magnesium ribbon was placed in the conical flask. 100 cm³ of dilute hydrochloric acid was added to the conical flask.

The mass of the flask and contents was measured at regular intervals. The loss in mass was calculated. Figure 7 shows a graph of the results.

Name the apparatus that could be used to measure out 100 cm³ of dilute hydrochloric acid.

Explain why there is a loss in mass of the flask and contents.

The graph shows that the rate of reaction slows as the reaction takes place.

Explain, in terms of particles, why the rate of reaction between magnesium ribbon and dilute hydrochloric acid slows as the reaction takes place.

The experiment was repeated using the acid at a higher temperature. All other conditions were kept the same.

State the effect of the higher temperature on the mass loss after two minutes.

The original experiment was repeated using the same mass of magnesium powder instead of the magnesium ribbon. All other conditions were kept the same.

Sketch, on the graph in Figure 7, the line you would expect for this experiment.

Some reactions are affected by the presence of a catalyst.

State the effect of a catalyst on a reaction.

Devise a simple experiment to find out what happens to the mass of a solid catalyst during a reaction.

Two compounds of barium are barium sulfide and barium chloride.

The hazard symbol shown in Figure 2 is on bottles containing barium metal.

State the meaning of this hazard symbol.

Give the names of the elements combined in barium sulfide.

Barium chloride is toxic.

Explain one safety precaution that should be taken when using barium chloride.

A beaker of barium chloride solution and a beaker of dilute sulfuric acid were placed on a balance, as shown in Figure 3.

The total mass reading on the balance was 25.7 g.

The dilute sulfuric acid was poured into the barium chloride solution and the beaker replaced on the balance, as shown in Figure 4.

Figure 4

The mixture formed contained a white precipitate.

State the total mass reading on the balance after the reaction.

Give the name of the white precipitate formed by the reaction of barium chloride solution with dilute sulfuric acid.

Solid sodium chloride is dissolved in water.

The sodium chloride solution is electrolysed in the apparatus shown in Figure 5.

State why sodium chloride solution, rather than solid sodium chloride, must be used in this experiment.

The formulae of the ions present in the sodium chloride solution are

Circle the ions that would be attracted to the anode.

Molten lead bromide can be electrolysed to form molten lead and bromine gas.

Explain how a student could modify the apparatus shown in Figure 5 to carry out this electrolysis.