Summative ENSCIMA _WED

Question 1.c: How would you make sure that the experiment/investigation you have conducted is a “fair test”?

Answer explanation

ØTo ensure a fair test has been done, firstly you would have to be sure that when changing one of the variables (the independent variable) to determine its effect on the dependent variable, all others have been kept constant. Secondly, you would have to make sure that all the measurements have been done accurately and repeated at least three times.

Question 1.e: Communicating results or Discussion is the final step of a scientific investigation. Why is it important?”

Answer explanation

ØThe final step in a scientific investigation is communicating what you have learned with others. This is a very important step because it allows others to test the hypothesis. If other researchers get the same results, they add support to the hypothesis. However, if they get different results, they may challenge or disprove the hypothesis.

Part a:

Question 2a: Two cups are filled with 50 mL of water. Ten drops of food coloring were placed in the first cup and one drop of the same food coloring was placed in the second cup. Describe the concentrations of the solutions produced in each cup.

Answer explanation

ØThe solution in the first cup containing 10 drops of food coloring in 50 mL water is more concentrated because it appears darker than the second. The solution in the second cup containing only one drop of food coloring in 50 mL water is less concentrated so it has a lighter appearance.

Question 3a: What is the percentage by mass of sodium chloride (NaCl) in a solution that is made by dissolving 5.5 grams of NaCl in 12.4 grams of water (H2O)?

Answer explanation

Question 3.b: A solution is known to be 30.7% by mass of sodium chloride in 12.4 g of water. What mass of sodium chloride was used to make this solution?”

Answer explanation

Question 4: Complete the table below to identify which of the materials B, C, D and E are mixtures elements or compounds by placing a tick (✓) or a cross (û) in the appropriate column (as shown for material A).

Answer explanation

An indicator is a dye that changes into a different color depending on whether it is in an acidic or basic substance. Many indicators come from plant sources and each of these has one color in an acid and a different color in a base.

Question 5a: Describe the steps that should be taken in determining whether a substance is acidic or basic using litmus paper.

Answer explanation

1. Prepare red and blue litmus paper. (Note: You may ask for litmus papers from your teacher.)

2. In a watch glass or any small container, put a small amount of the substance to be tested.

3. Get the litmus papers and tear each of them into three smaller pieces. Use one piece only for each substance to be tested.

4. Take one piece of the red litmus paper and dip it into the first substance to be tested.

ØIf the red litmus paper turns into blue, the substance is basic. If the blue litmus paper turns into red, the substance is acidic.

5. Take one piece of the blue litmus paper and dip it into the same substance.

6. Record the color changes in the litmus papers (if there are any) and dispose of the used litmus papers in the trash bin.

7. Repeat the same procedure for the remaining substances.

8. Using the recorded color changes, identify whether the substances are acidic or basic.

Question 6.c: Copper is a very common metal and Oxygen a very common non-metal. They have very different uses in our lives. Explain how their properties determine their use.

Answer explanation

ØCopper is a metal and like many other metals, is solid at room temperature. It is malleable and can be formed into fine wires. It is shiny and is a very good conductor of electricity and heat. Because of these properties it is used in electrical equipment and motors and in water pipes.

ØOxygen is a non-metal, and like many other non-mentals, is gas at room temperature. It is colorless and odorless. Oxygen is vital for all living things – animals need it to break down food to get energy; Plants give out oxygen as a waste product of the process of photosynthesis.

Question 7.a: Name three things that you know to be a liquid at room temperature

Answer explanation

Water, Milk, and Oil

Question 7c: Explain what happens to the motion and arrangement of particles when a substance undergoes the process of freezing?

Answer explanation

ØDuring freezing, the particles lose heat and therefore lose kinetic energy, so they begin to move more slowly. When the temperature is low enough, the particles no longer have enough energy to move freely in the liquid. They start to settle into fixed positions. The particles can vibrate about their fixed positions. They assume a definite shape, i.e., they become a solid.