1. Refer to the table below that shows the solubility of sugar in water at different temperatures:
|
Temperature (°C)
|
Solubility (g per 100 g water)
|
|
20
|
180
|
|
40
|
220
|
|
60
|
260
|
|
80
|
300
|
Based on the given data, determine the state of the resulting solution when 150 g of sugar is dissolved in 100 g of water at 40°C.
a) Saturated
b) Unsaturated
c) Supersaturated
d) Cannot be determined
Answer: b) If you dissolve 150 g of sugar in 100 g of water at 40°C, the solution is unsaturated. This is because the solubility of sugar at 40°C is 220 g per 100 g of water (as shown in the table), and since you've added only 150 g of sugar, there's still room for more sugar to dissolve before reaching the saturation point.
2. An experiment was conducted by passing a beam of light through different fluids. The observations were noted as follows:
- In fluid A, the path of light was clearly visible and appeared scattered.
- In fluid B, the path of light was not visible at all.
- In fluid C, the path of light was faintly visible but not scattered.
Based on the observations, which of the following statements is most likely to be true?
a) Fluid A is a true solution, fluid B is a colloid, and fluid C is a suspension.
b) Fluid A is a suspension, fluid B is a true solution, and fluid C is a colloid.
c) Fluid A is a colloid, fluid B is a true solution, and fluid C is a suspension.
d) Fluid A is a colloid, fluid B is a suspension, and fluid C is also a suspension.
Answer: c) The observations indicate the presence or absence of the Tyndall effect, which is the scattering of light by particles in a medium. Based on the given information:
Fluid A shows a scattered path of light, indicating the Tyndall effect. This suggests the presence of larger particles, characteristic of a colloid or suspension.
Fluid B does not show any visible path of light, indicating the absence of the Tyndall effect. This is a characteristic of a true solution, where the particles are very small and do not scatter light.
Fluid C shows a faintly visible path of light but is not scattered. This could be due to larger particles that are not uniformly dispersed, indicating a suspension.
3. If you have a solution of 250 mL of vinegar (acetic acid) dissolved in 750 mL of water, what is the volume-by-volume percentage of vinegar in the solution?
a) 25%
b) 33.3%
c) 50%
d) 75%
Answer: To calculate the volume-by-volume percentage of vinegar in the solution, you need to divide the volume of acetic acid by the total volume of the solution and then multiply by 100.
Volume of acetic acid = 250 mL
Volume of water = 750 mL
Total volume of solution = Volume of acetic acid + Volume of water = 250 mL + 750 mL = 1000 mL
Volume by volume percentage of vinegar = (Volume of acetic acid / Total volume of solution) × 100
Volume by volume percentage of vinegar = (250 mL / 1000 mL) × 100 = 25%
4. A student observes a piece of metal turning reddish-brown when exposed to air over time. This change is best explained by:
a) A physical change, as the metal's colour is altered without a new substance being formed.
b) A chemical change, where the metal reacts with oxygen to form a new compound on its surface.
c) Both a physical and chemical change occur simultaneously.
d) A reversible process since the metal can be restored to its original colour.
Answer: b) When a metal reacts with oxygen in the air, a process known as oxidation occurs. This reaction forms metal oxides on the surface of the metal. In the context described, the formation of a reddish-brown layer on the metal's surface indicates the presence of a metal oxide. This process is not simply a physical change, as the metal is actually reacting with oxygen to create a new substance (metal oxide) with different properties from the original metal. Therefore, the change is a chemical change rather than just a physical alteration of the metal's appearance.
5. When iron and sulphur powder are heated together, they combine to form a new substance with magnetic properties. What is this new substance?
a) A compound
b) An element
c) A mixture
d) An alloy
Answer: a) When iron and sulfur powder are heated together, they undergo a chemical reaction to form iron sulfide, which is a compound. Iron sulfide has different properties from both iron and sulfur, and it exhibits magnetic properties. This chemical change involves the rearrangement of atoms to create a new substance with distinct properties.
