Can some one answer my question for physical science for 9th grade

Starting with 250 mL of a 0.250 M solution of HBr; a) Calculate the initial pH of the solution.b) Calculate the pH after adding

maxonik [38]

Answer:

a.

pH = 0.602

b.

pH = 1.5

c.

pH = 7

d.

pH = 12.1

Explanation:

a ) To calculate the pH, use the following equation:

pH = -log [H+]

Hbr is a strong acid, so the [H+] concentration can be calculated as follow:

[HBr] = 0.250 M

As acid Hbr:

Hbr = H+ + Br-

As strong acid HBr dissociates at all, so

[HBr] = [H+] = 0.250 M

So the pH:

pH = -log [0.250 M] = 0.602

b) Calculate the pH after adding 250 mL of 0.125M NaOH

In this point, the reactions starts:

HBr + NaOH = H2O + NaBr

- First, we gonna find the mol of each reactant:

HBr:

mol = [M] × L

mol = 0.250 M × 0.250 L

mol = 0.0625 mol HBr

NaOH:

mol = [M] × L

mol = 0.125 M × 0.250L

mol = 0.03125 mol NaOH

In base on the reaction, it’s needed 1 mol of NaOH to neutralize 1 mole of HBr, so to neutralize 0.0625 moles of HBr its needed 0.0625 mol of NaOH:

0.0625 mol HBr – 0.03125 mol HBr = 0.03125 mol HBr

These are the moles free in the solution, and we going to use them to calculate the pH:

pH = -log [ H]

pH = - log [ 0.03125 ] = 1.5

c) Calculate the pH after adding 500 mL of 0.125M NaOH

NaOH:

mol = [M] × L

mol = 0.125 M × 0.500L

mol = 0.0625 mol NaOH

In base on the reaction, it’s needed 1 mol of NaOH to neutralize 1 mole of HBr, so to neutralize 0.0625 moles of HBr its needed 0.0625 mol of NaOH:

0.0625 mol HBr – 0.0625 mol HBr = 0 HBr

pH = 7

d) Calculate the pH after adding 600 mL of 0.125M NaOH.

NaOH:

mol = [M] × L

mol = 0.125 M × 0.600L

mol = 0.075 mol NaOH

In base on the reaction, it’s needed 1 mol of NaOH to neutralize 1 mole of HBr, so to neutralize 0.0625 moles of HBr its needed 0.0625 mol of NaOH:

0.075 mol NaOH – 0.0625 mol NaOH = 00125 NaOH

These are the moles free in the solution, and we going to use them to calculate the pH:

pOH = -log [ OH]

pOH = - log [ 0.0125 ] = 1.90

pH + pOH = 14

pH = 14- pOH = 14 – 1.90 = 12.1

4 0

3 years ago

Of the following reactions occurring at 25ºC, which one involves the greatest increase in entropy?H2(g) + Cl2(g) = 2 HCl(g)H2O(s

SVETLANKA909090 [29]

Answer: [tex]CO_2(s)\rightarrow CO_2(g)[/tex]

Explanation:

Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.

$\Delta S$ is positive when randomness increases and $\Delta S$ is negative when randomness decreases.

a) $H_2(g)+Cl_2(g)\rightarrow 2HCl(g)$

2 molesof gas are converting to 2 moles of another gas , thus $\Delta S$ is zero.

b) $H_2O(s)\rightarrow H_2O(l)$

1 mole of solid is converting to 1 mole of liquid, the randomness increases and thus $\Delta S$ is positive.

b) $Pb^{2+}(aq)+2Cl^-(aq)\rightarrow PbCl_2(s)$

2 moles of ions are converting to 1 mole of solid, the randomness decreases and thus $\Delta S$ is negative

d) $CO_2(s)\rightarrow CO_2(g)$

1 mole of solid is converting to 1 mole of gas, the randomness increases drastically and thus $\Delta S$ is highly positive.

3 0

3 years ago

Contour plowing, conservation plowing and crop rotation are ways to __________ soil. a. prevent c. lose b. conserve d. none of t

morpeh [17]

Explanation:

prevent becoz crop rotation means using it by planting the crop according to nuetrients so ur soil is prevented

8 0

3 years ago

Read 2 more answers

C2H6 is an example of what? a)iron b)element. c)atom. d)compound

Rama09 [41]

C2H6 is a chemical compound

6 0

3 years ago

Read 2 more answers

Why does the temperature of the water stay the same when it melts and boils?

krok68 [10]

The temperature stays the same when a solid changes to a liquid because energy is required to break the forces between particles of water therefore changing the state of matter and separating the particles away from each other.

When a liquid boils, the energy is needed by the particles to escape the surface of the liquid and boil. Instead of raising the temperature, the energy goes into the particles' kinetic energy store so it has enough speed to escape the surface of the liquid.

5 0

3 years ago