Chemical Effects of Electric Current quiz

Which of the following is a poor conductor of electricity?

An LED is preferred over a torch bulb in a tester because it:

In electroplating an iron spoon with copper, the spoon is connected to the:

When current is passed through water with carbon electrodes, the gas formed at the negative electrode is:

Iron cans used for storing food are electroplated with:

Depositing a layer of zinc on iron to protect it from rusting is called:

The needle of a magnetic compass placed near a wire carrying current is deflected because of the:

The solution used in the electroplating of copper is:

Electroplating is based on the:

The longer lead of an LED is connected to the:

Why is distilled water a poor conductor of electricity while tap water is a good conductor? (2 marks)

State two observations that show a chemical reaction is taking place at the electrodes when current passes through a solution. (2 marks)

Why is it dangerous to touch an electrical appliance with wet hands? (2 marks)

What is electroplating? Give two of its uses. (2 marks)

During copper electroplating, why does the blue colour of the copper sulphate solution not fade? (2 marks)

Why are car parts, bathroom taps and bicycle handlebars plated with chromium? (2 marks)

Why are iron objects such as bridges and pipes coated with zinc? (2 marks)

In the potato activity, what is observed near one of the wires, and what can the activity be used for? (2 marks)

What is an electrode? What can be used as electrodes in a simple school experiment on the electrolysis of water? (2 marks)

Why should used solutions from electroplating factories not be dumped into rivers or drains? (2 marks)

In a copper plating experiment, the mass of an object increased from 30.0 g to 30.6 g in 20 minutes. The copper plate initially weighed 25.0 g. Find the mass of the copper plate after 20 minutes, assuming all the copper transferred to the object. How much copper would be deposited in 1 hour at the same rate? (3 marks)

A student used a compass-needle tester for five liquids and recorded the deflection: salt solution 30 degrees, lemon juice 10 degrees, vinegar 12 degrees, sugar solution 0 degrees, distilled water 0 degrees. Arrange the liquids from best to poorest conductor and explain what a zero deflection indicates. (3 marks)

In an experiment on passing current through water, 30 mL of gas was collected at the negative electrode and 15 mL at the positive electrode in 10 minutes. Identify the two gases and the ratio of their volumes. What volumes would you expect after 20 minutes if the current stays the same? (3 marks)

A workshop silver-plates 120 spoons. Each spoon needs 0.5 g of silver. If silver costs Rs 90 per gram, find the total mass of silver used and its cost. Why is silver plating used instead of making the spoons of pure silver? (3 marks)

A student dissolved 1, 2 and 3 spoons of salt in equal volumes of distilled water and found compass deflections of 10, 18 and 25 degrees respectively. Describe the trend, explain it, and predict whether the deflection would be more or less than 25 degrees with 4 spoons of salt. (3 marks)

Read the passage and answer the questions. Boojho made a tester using a cell, a torch bulb and wires. When he dipped the free ends of the wires in lemon juice, the bulb did not glow. Paheli suggested that he replace the bulb with an LED, and then the LED glowed. (i) Does the first observation mean that lemon juice does not conduct electricity? Explain. (ii) Why did the LED glow when the bulb did not? (iii) Suggest one other way of detecting the weak current. (5 marks)

Read the passage and answer the questions. In a small factory, iron bathroom taps are chromium-plated to give them a shiny finish. The taps are dipped in a solution of a chromium compound and connected to the battery, and an electric current is passed for some time. (i) Why are the taps plated with chromium instead of being made of chromium? (ii) To which terminal of the battery are the taps connected? (iii) What precautions should the factory take in disposing of the used solution? (5 marks)

Read the passage and answer the questions. Paheli removed the carbon rods from two used cells, cleaned them and used them as electrodes. She placed them in a beaker of water to which a few drops of dilute sulphuric acid were added and connected them to a battery. Bubbles appeared on both rods. (i) Name the gases formed at the electrodes connected to the positive and negative terminals. (ii) Why are carbon rods suitable as electrodes? (iii) Why did she add the acid to the water? (5 marks)

Read the passage and answer the questions. A teacher gave Boojho a cell whose terminals were hidden under tape and two wires attached to them. He inserted the free ends of the wires about 1 cm apart into a fresh cut potato. After some time a greenish-blue spot appeared around one of the wires. (i) Which terminal is this wire connected to? (ii) What does the colour change show about the effect of current? (iii) How could Boojho use this activity to identify the positive terminal of the cell? (5 marks)

Read the passage and answer the questions. During heavy rain, an electrician warned the residents of a building not to touch electric switches with wet hands and to stay away from fallen electric wires lying in water. (i) Why does rain water or tap water conduct electricity? (ii) Why is pure distilled water a poor conductor? (iii) State two safety rules for using electrical appliances during the rainy season. (5 marks)

Draw a labelled diagram of a tester using an LED for testing liquids. Describe how you would use it to test lemon juice, vinegar, sugar solution and salt solution, state your expected observations, and explain why the free ends of the wires must not touch each other in the liquid. (6 marks)

Draw a labelled diagram of the set-up for copper plating an iron key. Describe the procedure, explain how copper is transferred from the plate to the key, state what happens to the mass of the plate and the key, and explain why a few drops of dilute sulphuric acid are added to the copper sulphate solution. (6 marks)

Draw a labelled diagram of the set-up for passing an electric current through water using carbon electrodes, with two test tubes collecting the gases. Name the gases collected at each electrode, give a simple test for each gas, and explain why this is a chemical effect of current. (6 marks)

Describe four applications of electroplating, naming the metal used and the reason in each case. Draw a labelled diagram of the cross-section of a tin-plated iron food can and explain why tin is preferred to zinc for food containers. (6 marks)

Draw a labelled diagram of a tester in which a wire carrying current is wound a few times around a magnetic compass. Explain why the compass needle deflects, how this tester is used to test liquids, and compare its sensitivity with that of a torch bulb tester. (6 marks)