Academic Master

Chemistry

Molar Mass Calculation

Forum Questions

Q1)

The formula for Molar mass is MM = grams/moles

The first step is to find moles. The formula to find it is:

PV = nRT (Odde, 2015)

Convert all the units into standard units.

P = 777 torr = 1.02 atm ; V = 125mL = 0.125L ; R = 0.082 K-1 L mol-1 atm; T = 126 C = 399.15 K

n = PV/RT = 0.00389276 mol

Since there are 0.281 grams, divide it by the number of moles to get the molar mass.

Molar Mass = grams/mol = 0.281/0.00389276 = 72 g/mol

Q2)

In order to find the volume of H2. The first step is to find the number of H2O moles. By using the formula n = m/M;

In order to find the number of moles, we will divide the mass, which is 15, by the molar mass of H20, which is 18 (1×2 + 2×8).

m = 15 and M = 18.

n = m/M = 15/18 = 0.8333.

After finding moles of H2, which is 0.8333, use the equation PV = nRT.

Convert all units into standard units.

P = 745 torr = 0.98 atm ; T = 20 C = 293 K ; R = 0.082 L atm K-1 mol-1

V = nRT/P = (0.833)*(0.0821)*(293) / 0.98 = 2.011 L

15g of H2O will produce 2.011 L of H2.

Lab 6 Assignment

Q1)

Titration is a process in which a titrant, which is a solution whose concentration is known, is added very slowly into a solution whose concentration is not known. This is done until the change of color takes place, which is also called neutralization. It is a method to find out how much solute is to be added in order for the reaction to happen.

Q2)

In the video, acid-base titration has been demonstrated. CH3COOH is acid, and NaOH is the base, and the process of titration is done between them.

Q3)

NaOH + CH3COOH = H2O + Na(CH3COO)

Q4)

The process shows that the acidic solution has CH3COO- and H3O+ ions, whereas the basic solution has Na+ and OH- ions, and when the acidic and basic solution combine, then these two opposite ions, i.e., negative and positive ions, are bound together with each other.

Q5)

The reactants used are acetic acid and sodium hydroxide.

Q6)

The glassware is a burette, which helps to take the measurement of the liquid more precisely and accurately. Sodium hydroxide was measured through it.

Q7)

The first step is to balance the equation. Then, a known concentration and volume of acid should be taken. Now, in order to get the moles of the acid, moles are to be found through molarity and acid volume. As the equation is balanced, the next step is to determine the ratio of moles. The equation we have is equal to one. Moles of the base in this balanced equation will be found and used in the reaction. For Example, 150mL of 0.100 moles CH3COOH to moles of NaOH. (150mL CH3COOH) x (0.100 moles CH3COOH/L CH3COOH) x (1L CH3COOH/1000mL CH3COOH) x (1 mole CH3COOH/ 1 mole NaOH) = 0.15 NaOH moles.

Q8)

The reaction between NaOH and CH3COOH is done with a ratio of 1:1. Equal moles are reacted. The concentration of CH3COOH in vinegar can be found by dividing the moles by the vinegar volume. For instance, the vinegar volume is 20mL. Then, we will get 0.89M CH3COOH. 1000mL/1L x 0.01778mol x 1/20mL = 0.89M.

Q9)

The cause of the solution being basic is the presence of OH-, and the cause of its acidity is H+. The reaction is acid-basic in nature, and so the reaction gives water and salt.

Q10)

The reaction is acid-basic in nature, and so the reaction gives water and salt.

Q11)

The pH of an acid can be found. The fusion of two two chemical substances with analyte and focus. Burette is used for titration purposes. The moles of analyte and titrant are equal from the equality focus. In a given test, the substance response’s purpose in the process of titration is the titrant’s focus, which is equal in a stoichiometric sense to the analyte’s moles.

pH = -log(H3O+)

= -log(8.9 x 10-1)

= -(-0.0506)

= 0.0506

Q12)

Dr. Yee’s demonstration showed that sodium hydroxide should be used to clean titration. One more thing that was demonstrated was that the valve was turned on and then off by the stopcock as soon as the liquid was added. Dr. Yee also cleared the tip if it was not cleared in order for the flow to be constant.

Q13)

The reaction between hydrochloric acid and limestone is:

CaCO3 + 2HCl = CO2 + H2O + Ca2

Q14)

When limestone reacts with the acid, it will give off gas bubbles. That is the first thing I will be looking for. If the reaction produces gas bubbles, it will mean that it is a reaction between carbonates (minerals or rock) and acid in it.

Q15)

C(NaOH) x V(base) = C(HCl) x V(acid)

C(HCl) = (39.25mL) (0.1522mol) / 35mL

= 0.170 mol HCl

Q16)

As soon as the color of the liquid changes to pink, this is the indication of the completion of the reaction.

Q17)

The name used by Dr. Yee is Phenolphthalein.

Q18)

The indicator is called Phenolphthalein, and it is used by adding it to the liquid. When the liquid changes its color to pink, then stop adding it.

Classmate Responses

Student # 1 Stephen

The first is done very accurately and effectively. The key to solving a question is first to find the correct answer, and another more effective way to do the question is to find the simplest way to answer any problem with the minimum steps. Question 1 is done with the minimum possible steps. The answer is correct, i.e. 12.1L. But the second question is incomplete. The way to answer that question is to write the balanced equation of the reaction first. The next step is to find the oxygen moles in the product part of the reaction (O2). Then you have to make sure all the units of pressure are the same I=Convert all of them into atm. Then, the final step is to use the gas law formula, which is PV = nRT. Rearrange the equation to find the volume. V = nRT/P. You will get your answer.

Student # 2 Steigwalker

The best way to solve a question is to first define all the known and unknown variables mentioned in the question. For instance, in the first question, the volume is to be found. Mention what V2 represents and similarly define what other variables mean. This should be done by giving the heading “Data” and then giving the heading of what it is there to find, which is V2. Then, give the heading to the solution and start solving it. This will give a neat look to your answer and make it easy for the teacher to check it. Also, highlight the answers. The answers are correct, but it would be better if every step was explained in one sentence or more so that the teacher would know you have done it by yourself.

References

Odde, D. J. (2015). Mitosis, diffusible crosslinkers, and the ideal gas law. Cell, 160(6), 1041–1043.

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