Question bank IMSO Science 2015

Editorial safety note: This is a teacher-supervised laboratory exercise. Do not taste unknowns, use test samples for cooking, or apply these reagents to skin. Use teacher-prepared dilute chemicals and eye protection. Record real observations only.

EXPERIMENT I : What are those white powders? Today is mother’s birthday. You want to cook an easy meal for her. It is your first time venture into her kitchen territory. Opening the seasoning shelf, you found five unlabeled jars which have different lid color. Each jar contains white or colorless solid. You kind of have an idea that they could be salt, sugar, baking soda, starch, and monosodium glutamate (MSG). Before start cooking anything, you must first figure out the identity of the solid in each jar. You do not dare to taste the unknown samples because you know that monosodium glutamate can trigger allergic symptoms. Luckily, there are some household chemicals, such as vinegar, Condy’s crystals solution and Tincture of iodine, that can help you solve the puzzle. Can you correctly identify the mystery powder?

Hints: 1. Vinegar is a common acid in the kitchen. Its reaction with base gives some bubbles. 2. Condy’s crystals solution (potassium permanganate, KMnO4) is used for wound cleansing. It turns from purple to brown when reacts with sugar, starch, and monosodium glutamate. 3. Tincture of iodine is an antiseptic. Iodine reacts with starch. The color changes from brown to purple color. 4. Solubility of MSG in water is better than that in vinegar.

Materials: 2 measuring spoons; 2 plastic droppers; 2 clear plastic plates; vinegar; iodine solution; Condy’s crystals solution (KMnO₄); water.

Procedures

1. Place one spoonful of each powder in each well of clear plastic plates.

2. Take the dropper and place 4 mL of water on each individual powder. Examine what happens? Do the powders dissolve? Write your observations in the result table.

3. Add 4 mL of water to another empty well as a blank for color comparison. Add 2 drops of Condy’s crystals solution to each unknown solution and the blank solution. Record your observations in the “Color test with KMnO₄” column.

4. Repeat steps 1–2. Then, add 2 drops of iodine solution to each unknown solution and a blank solution. Record your observations in the “Iodine test” column.

5. Repeat steps 1–2, but change from 4 mL of water to 4 mL of vinegar. Record what happens? Do the powders dissolve? Write your observations in the result table.

Caution: Iodine solution and Condy’s crystals solution should be handled with care.

EXPERIMENT I ANSWER SHEET

Write your observations in the result table. (15 points)

Indicate the solubility as the following: /// = all dissolved, // = partly dissolved, / = hardly dissolved.

| Unknown | Solubility in water | Solubility in vinegar | Color test with KMnO₄ | Iodine test | Identity |
| --- | --- | --- | --- | --- | --- |
| A | … | … | … | … | … |
| B | … | … | … | … | … |
| C | … | … | … | … | … |
| D | … | … | … | … | … |
| E | … | … | … | … | … |

Questions 1. Which powder undergoes a chemical reaction? Explain what supports your answer. (3 points)

Questions 2. What kind of gas in the reaction of vinegar with base? (1 point)

Questions 3. If you don’t have vinegar in the kitchen, what else can be used instead? Why? (1 point)

Editorial safety note: Work with teacher supervision, use only the supplied liquid, avoid splashes, and keep small metal balls away from mouths. All measurement cells remain blank until measured.

EXPERIMENT II Falling ball inside the liquid

Introduction

When a metal ball is dropped into a liquid, a viscous force will drag it. Naturally, this force is not constant but depends on the ball’s speed. The greater the speed, the greater the viscous force. In this experiment, a ball will be released just above the liquid surface, and after a while its speed will become constant called “terminal speed”. By intuition, one would expect that this terminal speed must be greater for a bigger ball because it is heavier. In this experiment, one wants to know exactly whether the terminal speed is proportional to (i) surface area of the ball ($4\pi r^2$) or (ii) the volume of the ball ($4\pi r^3/3$). To prove the proportionality, we need to plot a graph between two quantities on x-axis and y-axis respectively. When the plot of data has a linear tendency, i.e. fitted nicely with a linear line, one can say that they are proportional to one another.

Equipment and accessories 1 plastic bottle with unknown liquid 18 metal balls (6 sizes, 3 balls each) 1 stopwatch 1 magnet 2 rubber bands 1 ruler 2 graph papers Tissue paper

Experimental procedure

1. Wrap the plastic bottle with 2 rubber bands and set their position as the start and finish lines. Keep the start line about 60-70 mm below the liquid surface and the finish line as low as possible. Measure the distance between them with 1 mm precision.

2. Drop the ball less than 10 mm above the liquid surface and measure the time of falling between the start and finish lines. Leave the balls in liquid. Record your observation in the table.

3. Repeat this one more time and for all other provided ball sizes.

4. Calculate the terminal speed with two digit decimal in mm/s unit.

5. Plot your data on graph paper so that one can make conclusion whether the terminal speed is proportional to the surface area or the volume of the ball.

6. Answer questions 1–3 in your answer sheet.

Distance between the liquid surface and the start rubber band is … mm.

Distance between two rubber bands is … mm.

| No. | Surface area A (mm²) | Volume V (mm³) | Time trial 1 (s) | Time trial 2 (s) | Average time (s) | Terminal velocity (mm/s) |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 12.6 | 4.2 | … | … | … | … |
| 2 | 17.8 | 7.1 | … | … | … | … |
| 3 | 28.3 | 14.1 | … | … | … | … |
| 4 | 31.7 | 16.8 | … | … | … | … |
| 5 | 50.3 | 33.5 | … | … | … | … |
| 6 | 71.2 | 56.5 | … | … | … | … |

Plot your data on graph paper so that one can make conclusion whether the terminal speed is proportional to the surface area or the volume of the ball.

Question 1. Is the terminal speed proportional to the surface area or the volume of the ball? How do you make that conclusion? (1 point)

Question 2. From the information provided in the introduction, explain clearly why does the speed finally become constant? (2 points)

Question 3. If a student mistakenly set the start rubber band at the liquid surface, the speed will be too large or too small? Explain it. (2 points)

Students go on camping and making fire from a pile of wood. They gather around the fire to keep warm at night. It is a quiet night, clear sky and no wind. What is the heat transfer method from the fire to the students? (1 point)

A. Convection only

B. Radiation only

C. Conduction and convection

D. Convection and radiation

One plastic bottle is fully filled with water and the other one is empty. They are tightly closed and kept in a deep freezer. After one or two days, what will be your observations? 2.1 Bottle filled with water will … (0.5 point) 2.2 Bottle kept empty will … (0.5 point)

When a spiral paper was placed above a lighted candle, it started to spin after a short while. Which kind of energy is not relevant to this movement? (1 point)

If the size of the light source is getting smaller, how are the umbra and penumbra changing? (1 point)

A force F is applied to an L-shaped rod with length l on each side, which is hinged at P as shown. The force and L-shaped rod are on the same plane. In which diagram will F produce the greatest turning effect? (1 point)

An opera singer is singing with high pitch (frequency). What contributes to her high pitch singing? (1 point)

Rank the following materials (at room temperature) according to their sound speed from the lowest to the highest: (1 point) glass mercury air Answer: … < … < …

A picture of electrical wire connecting four resistors is shown as follows. The electrical wire is shielded by a plastic material and there is no short circuits between wires. What is the circuit diagram? (1 point)

A resistance of a copper bar is proportional to its length and inversely proportional to the cross-sectional area. Which of the following has the greatest resistance? (1 point)

Study the electrical circuit. All four bulbs are lighted up. Darcy wants to install a switch so that he is able to switch off TWO bulbs while leaving the rest of the bulbs lighted. Which part of the circuit S, T, U or V should Darcy install the switch? (1 point) Answer: …

The position vs. time graph below describes the motion of an athlete.

11.1 What is the velocity of the athlete at t = 2 s? (1 point)

11.2 What is the displacement of the athlete from t = 4 s to t = 7 s? (0.5 point)

11.3 What is the average speed from t = 0 s to t = 7 s? (0.5 point)

A successful conservation strategy should involve … (1 point)

Write down the scavengers from these group of organisms. (1 point) Vulture, Caterpillar, Fungi, Millipede, Termite, Grasshopper Answer: …

The consumption of the top [apex] predators, like shark, is discouraged due to the high accumulation of mercury present in their body, including shark fins. Why would consumption of these fish products be dangerous while it remained safe to consume other fish normally eaten by shark? (1 point)

The graph below is the absorption spectrum for an unknown substance. What is the color of this substance? (1 point)

Gilbert set up an experiment as shown below. Tank A and tank B were placed in the presence of sunlight while tank C and tank D were put into a wooden container. After an hour Gilbert measured the amount of carbon dioxide (CO2) in each tank. Which tank has the least amount of carbon dioxide? (1 point)

Biomass is a fuel that is developed from organic materials, a renewable and sustainable source of energy used to create electricity or other forms of power. Which genes would geneticists introduce into plant cells to generate genetically engineered plants with extra biomass? (1 point)

A. Genes supporting the mitochondrial function.

B. Genes accelerating the formation of plant cell wall.

C. Genes promoting the protein synthesis in cytoplasm.

D. Genes enhancing the accumulation of water in vacuole.

During the recent tsunami disaster a young child was separated from his/her biological parent in Sri Lanka. Years later with the help of a technique, the child was made to reunite with his/her parent. What technique is it? (1 point)