7.1 The Characteristic Properties of Acids & Bases

A student investigated the reaction of aqueous sodium hydroxide with aqueous solutions of two different acids, A and B.
Two experiments were done.

Experiment 1

Using a measuring cylinder, 50 cm³ of aqueous sodium hydroxide solution was poured into a polystyrene cup. The initial temperature of the solution was measured.

A burette was filled with the solution of acid A to the 0.0 cm³  mark.
5.0 cm³ of acid A was added to the aqueous sodium hydroxide in the cup and the mixture stirred.
The temperature of the solution was measured. Another 5.0 cm³  of acid A was added to the cup and the mixture stirred. The temperature of the mixture was measured.
More 5.0 cm³ portions of acid A were added to the cup until a total volume of 40.0 cm³ of acid had been added. After each addition, the mixture was stirred and the temperature measured.

Use the thermometer diagrams in the table to record the temperatures. 

The burette was emptied and rinsed with distilled water, and then with acid B. This acid was discarded. The burette was then filled up to the 0.0 cm³ mark with acid B.

Experiment 2

Experiment 1 was repeated using acid B instead of acid A.
Use the thermometer diagrams in the table to record the temperatures.

Plot the results for Experiments 1 and 2 on the grid and draw a smooth line graph for each experiment.
Clearly label your graphs.

Use your graph to estimate the temperature of the reaction mixture when 8.0 cm³  of acid B were added to 50 cm³ of aqueous sodium hydroxide.
Show clearly on the grid how you worked out your answer.

What type of chemical reaction, other than neutralisation, occurred when acid A reacted with sodium hydroxide?

Why was the burette rinsed firstly with distilled water and then with acid B before starting Experiment 2?

The solutions of acids A and B are the same concentration.

[1]

[1]

Describe one source of error in Experiment 2. Suggest one improvement to reduce this source of error.

source of error  ...........................................................................................................................
improvement ..............................................................................................................................

A student investigated the reaction of dilute hydrochloric acid with two different solids, calcium carbonate (marble) and calcium oxide.

Four experiments were carried out.

Experiment 1

By using a measuring cylinder, 50 cm³ of dilute hydrochloric acid was poured into a polystyrene cup and the initial temperature of the acid was measured.

2.5 g of small marble chips were added to the cup and the mixture stirred with the thermometer.

The temperature of the mixture was measured after 2 minutes.

Use the thermometer diagrams to record the temperatures in the table of results.

Experiment 2

Experiment 1 was repeated using 2.5 g of powdered calcium carbonate. Use the thermometer diagrams to record the results in the table.

Experiment 3

Experiment 1 was repeated using 1.5 g of lumps of calcium oxide. Use the thermometer diagrams to record the temperatures in the table.

Experiment 4

Experiment 1 was repeated using 1.5 g of powdered calcium oxide. Use the thermometer diagrams to record the results in the table.

What would be observed in Experiment 2?

Draw a bar chart of the results of the experiments on the grid below.

Which experiment produced

Give two reasons why the temperature changes are different in (d).

In Experiment 1, how would you know which reactant is in excess? Explain your answer.

Explain how the temperature changes would differ in the experiments if 100 cm³ of hydrochloric acid were used.

A student investigated the temperature changes that occur when two compounds A and B, react with hydrochloric acid. The apparatus below was used.

Experiment 1

By using a measuring cylinder, 30cm³ of hydrochloric acid was added to the plastic cup.

Use the thermometer diagram to record the initial temperature of the acid in the table. The timer was started, and some of the solid A was added to the cup. Immediate effervescence occurred. The mixture was stirred by moving the cup until the fizzing stopped.

More of A was then added and the student continued adding A in this way until all of solid A had been added.

Use the thermometer diagrams to record the temperature of the mixture every half minute.

Experiment 2

Experiment 1 was repeated using solid B. Use the thermometer diagrams to record the temperatures in the table.

Table of results

Experiment 1 

Experiment 2

Plot the results from both experiments on the grid below. For each set of results draw a smooth line graph. Indicate clearly which line represents Experiment 1 and which line Experiment 2.

From your graphs;

Suggest what type of compound solids A and B are. Explain your answer.

If the plastic cup and final reaction mixture are left for one hour, predict the temperature at this time for

Dilute nitric acid was added to a large amount of magnesium carbonate in a conical flask as shown.

The flask was placed on a balance and the mass of the flask and contents recorded every minute. The results are shown in the table.

Plot the results on the grid and draw a smooth line graph.

Which result appears to be inaccurate? Why have you selected this result?

Why does the mass of the flask and contents decrease?

Suggest the purpose of the cotton wool.

At what time did the reaction finish?

On the grid, sketch the graph you would expect if the experiment were repeated using nitric acid at a higher temperature.

Samples of concrete were placed in solutions of different pH. The graph shows the percentage corrosion of the samples.

Draw a smooth line graph on the grid.

Which point on the grid appears to be inaccurate? Explain your reason for identifying this point.

What happens to the percentage corrosion as the pH changes from 1 to 7?

Some plants do not grow well in acidic soil.

A farmer gives you a small sample of soil from a corner of one of his fields.

Plan an investigation to find out the pH of the soil sample.

You are provided with Universal Indicator solution and common laboratory apparatus.

What further experiments would be necessary to inform the farmer which plants should be grown in each of his fields?

An experiment was carried out to find the pH of samples of soil from a farmer’s field.

Identify the pieces of apparatus labelled

Why was the soil crushed?

Why should soil samples be taken from different parts of the field?

Suggest why it is important to know the pH of soil. 

A student investigated the neutralisation of dilute hydrochloric acid, using an excess of calcium carbonate.

Step 1 Excess calcium carbonate was added to hydrochloric acid.

Step 2. Excess calcium carbonate was removed from the solution.

Step 3. The solution of calcium chloride was tested with indicator paper.

Identify the pieces of apparatus labelled

What does the term excess mean?

Suggest the pH value of the solution of calcium chloride.

Acid base indicators

Indicators are used to identify acids and bases.
Indicators can be obtained from berries and other fruits. 

Plan an experiment to obtain an aqueous solution of an indicator from some berries.

Plan an experiment to use the indicator solution to show that it is an effective indicator.