General Chemistry Answers

name the compound NO3

calculate the mass of hydrogen when 25 grams of aluminum react with excess

A student weighs a rubber stopper and finds the mass to be 8.05 g. He places 20.0 mL of water into a graduated cylinder. After he drops the stopper into the graduated cylinder the volume increases to 25.5 mL. What is the volume of the rubber stopper?

Question options:

8.05 mL

Can't tell from the information given.

20.0 mL

5.5 mL

24.5 mL

A student obtains three liquids (A, B and C) in three separate test tubes. The densities for liquids A, B and C are found to be 2.3 g/mL, 0.95 g/mL and 0.67 g/mL respectively. Liquid A is poured into liquid B and two layers appear. Liquid A is poured into liquid C and two layers appear. Which statement is true?

Question options:

Liquid A appears on the top in both cases.

Liquids A and B are immiscible.

The specific gravity of A is less than the specific gravity of C.

The specific gravity of C is greater than the specific gravity of B.

Use Henderson Hasselback equation:

C. Bicarbonate Buffer

3. Prepare 100 mL of 0.200 bicarbonate buffer, pH 10 by calculating the mass of sodium

  bicarbonate and sodium carbonate.

    a. Use the Henderson-Hasselbalch equation to calculate the volume of each stock solution needed. pH = pKa + log [conjugate base] / [weak acid]1

 b. Check your calculations with other students. See the instructor if there is uncertainty.

c. Make the solution and check the pH of a portion of your

buffer solution using the pH meter.

       L = 245μL

3. Preparation of Bicarbonate Buffer

 Calculated Volume

CH₃COOH:    

KH₂PO4:        

Actual pH of the buffer: 

The Henderson Hasselback equation:

𝑝𝐻 = 𝑝𝐾𝑎 + log conj𝑢𝑔𝑎𝑡𝑒 𝑏𝑎𝑠𝑒 (𝐴) 𝑤𝑒𝑎𝑘 𝑎𝑐𝑖𝑑 (𝐻𝐴)

𝐵𝑢𝑓𝑓𝑒𝑟 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑂𝐻− 𝑜𝑟 𝐻3𝑂 + (𝑝𝐻 𝑐ℎ𝑎𝑛𝑔𝑒)(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑏𝑢𝑓𝑓𝑒𝑟 𝑖𝑛 𝐿)

Procedure:

C. Bicarbonate Buffer

3. Prepare 100 mL of 0.200 bicarbonate buffer, pH 10 by calculating the mass of sodium

bicarbonate and sodium carbonate.

a. Use the Henderson-Hasselbalch equation to calculate the volume of each stock solution needed.

pH = pKa + log [conjugate base] / [weak acid]1

b. Check your calculations with other students. See the instructor if there is uncertainty.

c. Make the solution and check the pH of a portion of your buffer solution using the pH meter.

L = 245μL

DATA:

Show your calculation:

3. Preparation of Bicarbonate Buffer

Calculated Volume

CH3COOH

KH2PO4

Actual pH of the buffer:

Procedure

1. Water as a universal solvent

a. Put about 0.5 grams of the following substances into six separate test tubes: NaCl, sugar, gelatin, margarine, ethanol.

b. Add 1 mL water to each test tube and shake vigorously to dissolve the substance. To substances that did not dissolve, add another 1 mL of water and shake again. Add another 1 mL to the solids that still not dissolve and shake again.

c. Repeat the solubility test using acetone instead of water.

2. Water as a good medium for biochemical reactions

a. Mix about 0.1 gram of dry, powdered citric acid and sodium bicarbonate (NaHCO3) in a dry test tube. Observe if a chemical reaction occurs.

b. Add about 10 mL of water to the mixture and note what happens

I. Find the solubility in WATER and solubility in ACETONE of the following:

1. NaCl

2. Sugar

3. Gelatin

4. Margarine

5. Ethanol

II. What are the reaction of Citric Acid and Sodium Bicarbonate?

1. In a biochemical assay, a chemist needs to add 2.93 g of glucose to a reaction mixture. Calculate the volume in mL of a 1.35M glucose solution she should use for the addition.

2. The concentrated sulfuric acid we use in the laboratory is 98.0 percent H₂SO₄ by mass. Calculate the molality and molarity of the acid solution. The density of the solution is 1.83g/mL

3. Calculate the pH if 0.30M Acetic Acid, with Ka = 1.8 x 10-5 is added to 0.20M Sodium Acetate.

4. On the laboratory shelf are 250mM solutions of both Acetic Acid and Sodium Hydroxide. How would you make a 100 ml solution of 25mM Acetate buffer of pH 5.50 using these stock solution?

1. A sample of 0.653 g of potassium chloride (KCl) is dissolved in 45.5 g of water. What is the percent by mass of KCl in the solution?

2. Calculate the molality of a sulfuric acid solution containing 34.2 g of sulfuric acid in

173 g of water. The molar mass of sulfuric acid is 98.09 g/mol.

3. How would you prepare a 1.8% NaBr (w:v) aqueous solution?

What is the molar mass of sodium carbonate?