Chemistry Entrance Exam

An experiment is planned to record the change in pH as a powdered base is added to 50 cm³ dilute hydrochloric acid.

The method suggested is:

step 1 add dilute hydrochloric acid up to the 50 cm³ mark on a beaker;

step 2 add one spatula of the base and stir;

step 3 measure the pH of the mixture;

step 4 repeat steps 2 and 3 until the pH stops changing.

State how you could change the method so that the amount of dilute hydrochloric acid can be measured more accurately.

• Use a conical flask

• Use a measuring cylinder

• Use a balance

• Use a beaker

An experiment is planned to record the change in pH as a powdered base is added to 50 cm³ dilute hydrochloric acid.

The method suggested is:

step 1 add dilute hydrochloric acid up to the 50 cm³ mark on a beaker;

step 2 add one spatula of the base and stir;

step 3 measure the pH of the mixture;

step 4 repeat steps 2 and 3 until the pH stops changing.

State how you could change the method so that the amount of the base can be measured more accurately.

• Use a conical flask

• Use a measuring cylinder

• Use a balance

• Use a beaker

An experiment is planned to record the change in pH as a powdered base is added to 50 cm³ dilute hydrochloric acid.

During the experiment the pH changes from 2 to 10.

If phenolphthalein indicator is added at the beginning of the experiment, a colour change occurs as the base is added.

State the colour change that occurs.

• colourless to magenta

• magenta to colourless

• colourless to orange

• orange to colourless

Calcium nitrate solution can be made by adding solid calcium carbonate to dilute nitric acid in a beaker.

The solid calcium carbonate is added until some remains at the bottom of the beaker.

After this reaction the liquid in the beaker is:

• Acidic

• Alkaline

• Neutral

• Pure water

Calcium nitrate solution can be made by adding solid calcium carbonate to dilute nitric acid in a beaker.

The solid calcium carbonate is added until some remains at the bottom of the beaker.

Select two reasons why the calcium carbonate is added until some solid remains at the bottom of the beaker.

• To react all of the nitric acid in the solution

• To react all of the calcium carbonate in the solution

• So that the calcium nitrate is pure

• So that the calcium carbonate is pure

A student set up the apparatus shown in Figure above to obtain pure water from sea water by distillation.

Explain how the water in sea water separates to produce the pure water in this apparatus.

• The water condenses to form water vapour, leaving the salt behind. The water vapour evaporates to form pure water.

• The water evaporates to form water vapour, leaving the salt behind. The water vapour condenses to form pure water.

• The sea water evaporates to form water vapour. The sea water vapour condenses to form pure water.

• The sea water evaporates to form water vapour, leaving the salt behind. The sea water vapour condenses to form pure water.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

A student set up the apparatus shown in Figure above to obtain pure water from sea water by distillation.

Explain how the apparatus could be improved to increase the amount of pure water collected from the same volume of sea water.

• Use a Liebig condenser to ensure all of the sea water vapour condenses.

• Use anti-bumping granules.

• Use a fractionating column.

• Use a Liebig condenser to increase the effectiveness of cooling.

Tags

NGSS.MS-ETS1-4

NGSS.MS-PS3-3

Copper sulfate solution was electrolysed using copper electrodes. Before the electrolysis, the masses of the electrodes were determined.

After the electrolysis, the electrodes were washed and dried and their masses re-determined.

The table above shows these masses and the resulting changes in masses of the electrodes.

Choose the answer that best explains these results.

• The anode has lost copper and the cathode has gained copper. At the anode, copper atoms become copper ions and lose two electrons. At the cathode, copper ions become copper atoms and gain two electrons.

• The anode has gained copper and the cathode has lost copper. At the anode, copper atoms become copper ions and gain two electrons. At the cathode, copper ions become copper atoms and lose two electrons.

• The anode has lost copper and the cathode has gained copper. At the anode, copper ions become copper atoms and gain two electrons. At the cathode, copper atoms become copper ions and lose two electrons.

The apparatus shown above was used to electroplate a spoon with nickel.

State to what the anode and cathode have to be connected in order to carry out the electroplating.

• electrolyte

• cathode

• battery

• anode

The apparatus shown above was used to electroplate a spoon with nickel.

Predict the name of a substance that could be dissolved in water to form the electrolyte for this electroplating.

• nickel

• nickel chloride

• copper chloride

• copper

Tags

NGSS.HS-PS2-5