1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
BartSMP [9]
3 years ago
9

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.
Chemistry
1 answer:
DanielleElmas [232]3 years ago
4 0

Answer:

pH = 11.30

Explanation:

The reaction of HCN with NaOH is:

HCN + NaOH → H₂O + Na⁺ + CN⁻

<em>Where 1 mole of hydrocyanic acid reacts with 1 mole of NaOH.</em>

<em> </em>

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) = <em>0.252M CN⁻ </em>

<em />

This, CN⁻ is in equilibrium with water thus:

CN⁻(aq) + H₂O(l) ⇄ HCN(aq) + OH⁻(aq)

Where Kb is:

Kb = [HCN][OH⁻] / [CN⁻] <em>(1)</em>

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

<em>pH = 11.30</em>

You might be interested in
Gizmo Student Exploration: Periodic Trends awner key, Please I need help with this as soon as possible! I have attached what I h
Vlad [161]

Answer:

I cant see it

Explanation:

6 0
3 years ago
Resistance of a material being scratched in known as
Wittaler [7]
Resistance of a material being scratched in known as: Hardness
3 0
3 years ago
Read 2 more answers
hydrogen decomposes quickly when exposed to light. the reaction for decomposing hydrogen peroxide is:
Svet_ta [14]

The decomposition reaction for hydrogen peroxide is given below:

                                     2H_{2} O_{2} → 2H_{2} O + O_{2}

This is a decomposition reaction.

Reactions in which a reactant breaks into two or more products are known as Decomposition reactions.

                                          AB → A + B

here, AB represents the reactant that begins the reaction, and A and B represent the products of the reaction

The decomposition reaction of decomposing hydrogen peroxide is exothermic. When the hydrogen peroxide undergoes a decomposition reaction, heat is also released along with water and oxygen.

Hence the  reaction for decomposing hydrogen peroxide is :

         2H_{2} O_{2} → 2H_{2} O + O_{2}

If you need to learn more about Decomposition reaction, click here

brainly.com/question/16987748?

#SPJ4

5 0
1 year ago
It's actually Science but I didn't find it.
fomenos

Answer:

Forces acting on an object may be balanced or unbalanced. When the forces  acting on an object have <u>equal</u> strength and act in opposite directions, they  are <u>balanced</u>. These forces cancel out one another, and the <u>motion</u> of the  object does not <u>change</u>.  When the forces acting on an object are <u>unbalanced</u>, they do not cancel out  one another. An unbalanced force acting on an object results in the object’s  motion <u>changing</u>. The object may change its <u>speed</u> (speed up or slow down), or it may change its <u>direction</u>.  <u>Friction</u> is a force that resists the motion or the tendency toward motion  between two objects in contact with each other.  <u>Gravity</u> is a force that pulls objects toward one another. For example, Earth  pulls all objects toward it.

Explanation:

3 0
3 years ago
The radioisotope phosphorus-32 is used in tracers for measuring phosphorus uptake by plants. The half-life of phosphorus-32 is 1
Harman [31]

Answer:

54 days

Explanation:

We have to use the formula;

0.693/t1/2 =2.303/t log Ao/A

Where;

t1/2= half-life of phosphorus-32= 14.3 days

t= time taken for the activity to fall to 7.34% of its original value

Ao=initial activity of phosphorus-32

A= activity of phosphorus-32 after a time t

Note that;

A=0.0734Ao (the activity of the sample decreased to 7.34% of the activity of the original sample)

Substituting values;

0.693/14.3 = 2.303/t log Ao/0.0734Ao

0.693/14.3 = 2.303/t log 1/0.0734

0.693/14.3 = 2.6/t

0.048=2.6/t

t= 2.6/0.048

t= 54 days

3 0
3 years ago
Other questions:
  • 1. What volume of toluene do you need to add to 1 mL of ethyl acetate to make an equi-molar mixture? The density of ethyl acetat
    11·1 answer
  • Nitric acid is usually purchased in concentrated form with a 70.3% HNO3HNO3 concentration by mass and a density of 1.41 g/mLg/mL
    11·1 answer
  • If a solution is saturated, which of these is true?
    12·2 answers
  • Which value gives the number of particles in 1 mol of a substance?​
    11·1 answer
  • A pure sample of a new chemical compound was analyzed and was found to have the following mass percentages: Al 31.5 %; O 56.1 %;
    9·1 answer
  • Yo please help I will give you 10 points PLEASE
    10·1 answer
  • The initial velocity of a car is 10 m/s to the north. The car undergoes an acceleration of 2 m/sto the north for 4 seconds. What
    11·1 answer
  • Calculate the energy of light with a frequency of 5.21 x 104 Hz
    12·1 answer
  • Help me guys plzlzlz
    15·2 answers
  • How many grams sodium bromide can be formed from 51 grams of sodium hydroxide?
    5·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!