Chemistry, 14.04.2020 18:14 justiceisbae1

A chemist titrates 120.0 mL of a 0.4006 M hydrocyanic acid (HCN) solution with 0.6812 MNaOH solution at 25 °C. Calculate the pH at equivalence. The pKa of hydrocyanic acid is 9.21.

Answers: 3

Show answers

Answers

Answer from: makenziehook8

pH = 11.30

Explanation:

The reaction of HCN with NaOH is:

HCN + NaOH → H₂O + Na⁺ + CN⁻

Where 1 mole of hydrocyanic acid reacts with 1 mole of NaOH.

Moles of HCN are:

0.1200L × (0.4006mol / L) = 0.04807moles HCN

Thus, at equivalence, moles of NaOH you must add are 0.04807moles. And you must add:

0.04807moles × (1L / 0.6812mol) = 0.07057L of the 0.6812M NaOH solution.

Concentration of CN⁻ at equivalence point is:

0.04807moles / (0.1200L + 0.07057L) = 0.252M CN⁻

This, CN⁻ is in equilibrium with water thus:

CN⁻(aq) + H₂O(l) ⇄ HCN(aq) + OH⁻(aq)

Where Kb is:

Kb = [HCN][OH⁻] / [CN⁻] (1)

Kb = Kw / Ka

Ka is -log pKa → 6.166x10⁻¹⁰

Kb = 1x10⁻¹⁴ / 6.166x10⁻¹⁰ = 1.62x10⁻⁵

Concentrations in equilibrium are:

[CN⁻] = 0.252M - X

[HCN] = X

[OH⁻] = X

Replacing in (1):

1.62x10⁻⁵ = [X][X] / [0.252M - X]

4.08x10⁻⁶ - 1.62x10⁻⁵X = X²

0 = X² + 1.62x10⁻⁵X - 4.08x10⁻⁶

Solving for x:

X = -0.002 → False answer. There is no negative concentrations.

X = 0.00201 → Right answer.

As [OH⁻] = X; [OH⁻] = 0.00201

pOH is -log [OH⁻]

pOH = 2.70

As 14 = pOH + pH

pH = 11.30

Answer from: Quest

The answer to your question really depends on three things: how much water you have, how cold it is to start out, and how cold the things around it are. water actually freezes when it gets to 32 degrees fahrenheit (0 degrees celsius), but the time it takes to get there may be different. let's start with the first. if you take two glasses, and fill one with a tiny bit of water, and the other about halfway, then put them both in the freezer, the one with less water will freeze first (you can try this at home, but i recommend using plastic cups and not glass ones). now let's move on to the second part. let's say you have two glasses, and you fill one with really cold water that has been in the refrigerator, and the other with really hot water from the sink. if you put both of them in the freezer, the one that started out colder will freeze first. for the third part, let's imagine that you have two glasses with the same amount of water in them, and the water is at the same temperature. imagine putting one outside on a really really cold day in georgia, and having a friend in alaska put one outside on the same day. since it would be so much colder in alaska, the glass of water there would freeze before yours. so, if you took a tiny bit of really cold water in a glass, and put it outside on a cold day in alaska, it would freeze a lot faster than a big glass of hot water outside on a cold day in georgia.

Answer from: Quest

The correct answer is b.hoped i you

Another question on Chemistry

Chemistry, 22.06.2019 04:00

Mitosis is a type of cell division that produces cells that are identical to the parent cell. meiosis is a different type of cell division that produces cells that carry have a genetic material of the parent cell. based on the information provided how do the purpose of mitosis and meiosis differ

Answers: 3

Answer

Chemistry, 22.06.2019 04:30

Which is a chemical property of iron? a. it forms iron oxide (rust) when exposed to moisture and air. b. it is a gray–black metal that is hard to the touch. c. it has a melting point of 2795°f (1536°c). d. it is a good conductor of heat

Answers: 2

Answer

Chemistry, 22.06.2019 07:00

6what is the importance of water on earth? a) it keeps the top layer of the geosphere cool b) it allows life to exist c) it provides ice at the poles d) it creates earth's blue color from space

Answers: 2

Answer

Chemistry, 22.06.2019 07:50

Many reactions take place in aqueous solution. when potential reactants are mixed, a reaction will occur if there is some driving force that favors the formation of products. it is often convenient to categorize reactions in terms of these driving forces: precipitate formation, in which an insoluble solid is formed, weak electrolyte formation, as in a neutralization reaction involving water, or transfer of electrons, as in a redox reaction. these reactions can be represented by full molecular equations, which contain all species in the reaction mixture, or by net ionic equations, which show only the species that actually undergo a change. the latter does not contain the spectator ions, which do not undergo a net change or do not take part in the reaction. part a when the following two solutions are mixed: k2co3(aq)+fe(no3)3(aq) the mixture contains the ions listed below. sort these species into spectator ions and ions that react. drag the appropriate items to their respective bins. view available hint(s) spectator ions ions that react part b what is the correct net ionic equation, including all coefficients, charges, and phases, for the following set of reactants? assume that the contribution of protons from h2so4 is near 100 %.ba(oh)2(aq)+h2so4(aq)→ express your answer as a chemical equation. view available hint(s) nothing provide feedback

Answers: 3

Answer

You know the right answer?

A chemist titrates 120.0 mL of a 0.4006 M hydrocyanic acid (HCN) solution with 0.6812 MNaOH solution...

Questions