Year 7 Chemistry HW Questions

Transcription

1 Year 7 Chemistry HW Questions 37 minutes 56 marks Page 1 of 15

2 Q1. Molly used a ph sensor to test different liquids. She dipped the probe of the sensor into each liquid and recorded the ph value in a table. (a) In the table below, tick one box for each liquid to show whether it is acidic, neutral or alkaline. One has been done for you. liquid ph value acidic neutral alkaline alcohol 7 dilute hydrochloric acid 2 distilled water 7 vinegar 3 sodium hydroxide solution 11 2 marks (b) Between each test Molly dipped the probe into distilled water. Why did she do this? Which other liquid in the table could Molly use between tests to have the same effect as distilled water? Page 2 of 15

3 (c) Molly put a piece of magnesium into a test-tube containing 20 cm 3 of vinegar. She put another piece of magnesium into a test-tube containing 20 cm 3 of dilute hydrochloric acid. Molly thought that magnesium would react more vigorously with hydrochloric acid than with vinegar. What information in the table made Molly think this? How would Molly be able to tell if a more vigorous reaction took place with hydrochloric acid than with vinegar? (d) Complete the word equation for the reaction between magnesium and hydrochloric acid. magnesium + hydrochloric acid 2 marks After some time this reaction stopped. Why did the reaction stop? maximum 9 marks Page 3 of 15

4 Q2. Hydrochloric acid is a strong acid. (a) Winston used universal indicator solution to find the ph of some hydrochloric acid. Suggest the colour of the mixture of universal indicator solution and the hydrochloric acid.... Suggest the ph of the hydrochloric acid.... (b) Indigestion can be caused when too much hydrochloric acid is produced in the stomach. Magnesium carbonate can be used to treat indigestion. Winston crushed some indigestion tablets containing magnesium carbonate. He added them to hydrochloric acid in a test-tube. The mixture fizzed. The word equation for the reaction is shown below. magnesium + hydrochloric magnesium + carbon + water carbonate acid chloride dioxide Use the word equation to explain why the mixture fizzed when the reaction took place. Winston continued to add crushed tablets to the acid until the mixture stopped fizzing. Why did the fizzing stop? Page 4 of 15

5 (c) When magnesium carbonate reacts with hydrochloric acid, magnesium chloride is formed. Which two words describe magnesium chloride? Tick the two correct boxes. a compound a mixture an element a salt a metal a solvent 2 marks (d) It is important that the hydrochloric acid in the stomach is not completely neutralised by indigestion tablets. Why is hydrochloric acid needed in the stomach? maximum 7 marks ## Some crushed ice at 20 C was placed in a beaker. A thermometer was put into the ice, and the beaker was heated gently for 15 minutes. Page 5 of 15

6 The graph shows how the reading on the thermometer changed over the 15 minutes. (a) By how much did the temperature in the beaker change during the 15 minutes?... C (b) Which letter on the graph shows: when the ice is melting?... when the water is boiling?... (c) During the experiment, the beaker and its contents were quickly removed from the heat and weighed on a balance at the following times. at 0 minutes at 5 minutes at 10 minutes at 15 minutes Page 6 of 15

7 At which two times would you expect the readings on the balance to be the same?... minutes and... minutes Between which two of these times was the mass of the contents of the beaker changing most rapidly?... minutes and... minutes Maximum 5 marks Q4. Sarah wanted to find out how the length of a copper rod changes when it is heated. She fixed one end of the rod and allowed the other end to roll on a pin which had been put on a glass plate. A drinking straw, attached to the pin, showed the movement of the end of the rod. (a) What happens to the motion of the copper atoms in the rod as it is heated? What happens to the average distance between the atoms of copper when the rod is heated? Page 7 of 15

8 (b) The graph shows the length of a copper rod at different temperatures. The rod was mm long at room temperature. At what temperature has the rod increased its length by 1.0 mm? C The rod was mm long at room temperature. What will its length become if it is placed in melting ice at 0 C? mm Maximum 4 marks Q5. Sue pumps up a bicycle tyre. As she does so, she notices that the pump becomes hot. (a) Where, and how, was the energy stored before it was transferred in pumping up the tyre?... Page 8 of 15

9 (b) Explain how the gas molecules inside the tyre exert pressure on the walls of the tyre (c) The air going into the tyre was warmed up by the pumping. What effect will this have on the motion of gas molecules in the air in the tyre? (d) When the air in the tyre becomes hotter, the pressure rises. Give one reason, in terms of the motion of gas molecules in air, why the pressure rises (e) The pressure in the tyre increases as Sue forces more air into the tyre. Explain why a larger number of gas molecules increases the pressure in the tyre Maximum 5 marks Q6. (a) The table below shows information about five elements. element melting point ( C) boiling point ( C) conducts electricity colour A 7 59 no brown B no colourless C yes silvery D no yellow E yes orange Which two of these elements are likely to be metals? Write the letters.... and... Page 9 of 15

10 Which element in the table is liquid at room temperature? Write the letter.... (b) What is the chemical symbol for copper? Tick the correct box. Cr Cu C Co Ca (c) How many atoms of iron and oxygen are there shown in the formulas for FeO and Fe 2 O 3? Complete the table below. compound FeO number of atoms of iron number of atoms of oxygen Fe 2 O 3 2 marks maximum 5 marks Q7. Ben put a beaker weighing 50 g on a balance. He added 50 g of dilute hydrochloric acid and 2.5 g of calcium carbonate to the beaker. The total mass of the beaker and its contents was g. Page 10 of 15

11 (a) The hydrochloric acid reacted with the calcium carbonate. How could Ben tell that a chemical reaction was taking place in the beaker? (b) The word equation for the reaction which took place is: hydrochloric acid + calcium carbonate calcium chloride + carbon dioxide + water When the reaction stopped, the total mass had decreased from g to g. Some water had evaporated from the beaker. What else caused the drop in mass? Use the word equation to help you answer the question (c) When the reaction stopped, Ben tested the contents of the beaker with universal indicator paper. The calcium carbonate had neutralised the acid. What is the colour of universal indicator paper in a neutral solution?... (d) Which two materials in the list below are mainly calcium carbonate? Tick the two correct boxes. coal glass limestone marble sandstone 2 marks Page 11 of 15

12 (e) Metals react with acids. What gas is produced when a metal reacts with an acid?... Maximum 6 marks Q8. The graph shows how the solubility of two salts in water changes with temperature. The solubility is the number of grams of the salt which will dissolve in 100 g of water. (a) Describe how the solubility of copper sulphate changes with temperature (b) Use the information in the graph to answer the questions below. What is the solubility of potassium chloride at 40 C?. g per 100 g of water At what temperature are the solubilities of the two salts the same?. C Page 12 of 15

13 (iii) What is the largest mass of copper sulphate which can be dissolved in 50 g of water at 60 C? (c) Why is the solubility of salts in water normally given only for temperatures between 0 C and 100 C? marks Maximum 6 marks Q9. (a) The apparatus in the diagram below is used to obtain pure water from impure water. What temperature would the thermometer show? C Page 13 of 15

14 What is the function of the piece of apparatus labelled R? (iii) Give the name of the process which purifies water in this way. (b) The diagram below shows particles in a gas, a solid and a liquid. Each arrow, A, B, C and D, represents a change of state. Choose from the following words to complete the sentences below. boiling condensing distilling evaporating filtering freezing melting Change of state A is called. Change of state B is called. Change of state C is called. Change of state D is called. 4 marks Look back to the apparatus in part (a). Give the letter, A, B, C or D, from the diagram above, for the change of state which occurs: in the round-bottomed flask in the piece of apparatus labelled R.. 2 marks Maximum 9 marks Page 14 of 15

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