Q27. The density of a rock is measured by volume displacement of water and the images of the measurement done in a graduated cylinder are given below. The mass of the rock is 78.45 g. From the images, report the volume of water and calculate the density of the rock. Give the correct number of significant figures in all your answers.

Background

Topic: Density and Volume by Water Displacement

This question tests your understanding of how to determine the density of an irregularly shaped object using the water displacement method. You will use the change in water volume to find the volume of the rock, then use the mass and volume to calculate density.

Key Terms and Formulas

• Density (): The mass per unit volume of a substance.

• Water Displacement: The volume of water displaced by the rock equals the volume of the rock.

Key formulas:

• Volume of rock = Final volume (with rock) – Initial volume (without rock)

Step-by-Step Guidance

1. Examine the graduated cylinder images to determine the initial and final water volumes. Read the bottom of the meniscus for each measurement.

2. Calculate the volume of the rock by subtracting the initial water volume from the final water volume.

3. Record the mass of the rock (given as 78.45 g).

4. Use the density formula to set up the calculation for the density of the rock. Be sure to keep track of significant figures based on the measurements provided.

5. To convert the density from g/mL to kg/m3, use the conversion factor: .

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Q28. From the images of the buret given below, what is the initial buret reading for the titration? What is the final reading? How much liquid was dispensed? (4 points) Give the correct number of significant figures. Is buret a TC only glassware or a TD only glassware or both?

Background

Topic: Laboratory Measurements – Buret Readings

This question tests your ability to accurately read a buret, calculate the volume of liquid dispensed, and understand the function of laboratory glassware (To Contain vs. To Deliver).

Key Terms and Formulas

• Buret: A piece of volumetric glassware used to deliver precise volumes of liquid, typically in titrations.

• TD (To Deliver): Glassware calibrated to deliver a specific volume.

• Volume dispensed: Final reading – Initial reading

Step-by-Step Guidance

1. Carefully read the initial and final buret readings from the images, making sure to read at the bottom of the meniscus and record to the correct number of decimal places.

2. Subtract the initial reading from the final reading to determine the volume of liquid dispensed.

3. Consider the function of a buret: is it designed to contain (TC) or to deliver (TD) a measured volume?

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Q29. Given below is the standard curve for the absorbances for various concentration of a compound. The concentration is in mg/L. Answer the questions below based on the graph. (3 points)

• Which is the independent variable?

• What will be the absorbance of a solution that has a concentration of 8.73 mg/L? Give 3 sig figs in your answer.

Background

Topic: Spectrophotometry and Standard Curves

This question tests your understanding of how to interpret a standard curve and use it to determine the absorbance of a solution at a given concentration. It also checks your knowledge of independent and dependent variables in an experiment.

Key Terms and Formulas

• Standard Curve: A plot of absorbance (y-axis) versus concentration (x-axis) used to determine unknown concentrations.

• Independent Variable: The variable that is changed or controlled in a scientific experiment (here, concentration).

• Equation of the line: (where is absorbance and is concentration in mg/L)

Step-by-Step Guidance

1. Identify the independent variable by looking at the x-axis of the graph.

2. To find the absorbance for a concentration of 8.73 mg/L, substitute into the equation .

3. Set up the calculation, but do not compute the final value yet. Remember to keep three significant figures in your answer.

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Q26. Write the correct name for the glassware given below:

Background

Topic: Laboratory Equipment Identification

This question tests your ability to recognize and correctly name common laboratory glassware used in chemistry labs.

Key Terms

• Erlenmeyer Flask: A conical flask used for mixing, heating, and storing liquids.

Step-by-Step Guidance

1. Observe the shape and markings of the glassware in the image.

2. Recall the distinguishing features of an Erlenmeyer flask: conical body, flat bottom, narrow neck, and volume markings.

3. Write the correct name for this piece of glassware.

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