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marin [14]
2 years ago
13

How many molecules are in 643.21 grams of Mg3(PO4)2?

Chemistry
1 answer:
Eva8 [605]2 years ago
4 0

Answer:

643.21g  1 mol  6.022^23

262.87 g   1 mol

= 1.4735E24     [Mg3(PO4)2]

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100.00 mL of 0.15 M nitrous acid (HNO2) are titrated with a 0.15 M NaOH solution. (a) Calculate the pH for the initial solution.
wolverine [178]

Answer:

a. pH = 2.04

b. pH = 3.85

c. pH = 8.06

d. pH = 11.56

Explanation:

The nitrous acid is a weak acid (Ka = 5.6x10⁻⁴) that reacts with NaOH as follows:

HNO₂ + NaOH → NaNO₂(aq) + H₂O(l)

a. At the beginning there is just a solution of 0.12M HNO₂. As Ka is:

Ka = [H⁺] [NO₂⁻] / [HNO₂]

Where [H⁺] and [NO₂⁻] ions comes from the same equilibrium ([H⁺] = [NO₂⁻] = X):

5.6x10⁻⁴ = X² / 0.15M

8.4x10⁻⁵ = X²

X = [H⁺] = 9.165x10⁻³M

As pH = -log [H⁺]

<h3>pH = 2.04</h3><h3 />

b. At this point we have HNO₂ and NaNO₂ (The weak acid and the conjugate base), a buffer. The pH of a buffer is obtained using H-H equation:

pH = pKa + log [NaNO₂] / [HNO₂]

<em>Where pH is the pH of the buffer,</em>

<em>pKa is -log Ka = 3.25</em>

<em>And [NaNO₂] [HNO₂] could be taken as the moles of each compound.</em>

<em />

The initial moles of HNO₂ are:

0.100L * (0.15mol / L) = 0.015moles

The moles of base added are:

0.0800L * (0.15mol / L) = 0.012moles

The moles of base added = Moles of NaNO₂ produced = 0.012moles.

And the moles of HNO₂ that remains are:

0.015moles - 0.012moles = 0.003moles

Replacing in H-H equation:

pH = 3.25 + log [0.012moles] / [0.003moles]

<h3>pH = 3.85</h3><h3 />

c. At equivalence point all HNO2 reacts producing NaNO₂. The volume added of NaOH must be 100mL. That means the concentration of the NaNO₂ is:

0.15M / 2 = 0.075M

The NaNO₂ is in equilibrium with water as follows:

NaNO₂(aq) + H₂O(l) ⇄ HNO₂(aq) + OH⁻(aq) + Na⁺

The equilibrium constant, kb, is:

Kb = Kw/Ka = 1x10⁻¹⁴ / 5.6x10⁻⁴ = 1.79x10⁻¹¹ = [OH⁻] [HNO₂] / [NaNO₂]

<em>Where [OH⁻] = [HNO₂] = x</em>

<em>[NaNO₂] = 0.075M</em>

<em />

1.79x10⁻¹¹ = [X] [X] / [0.075M]

1.34x10⁻¹² = X²

X = 1.16x10⁻⁶M = [OH⁻]

pOH = -log [OH-] = 5.94

pH = 14-pOH

<h3>pH = 8.06</h3><h3 />

d. At this point, 5mL of NaOH are added in excess, the moles are:

5mL = 5x10⁻³L * (0.15mol / L) =7.5x10⁻⁴moles NaOH

In 100mL + 105mL = 205mL = 0.205L. [NaOH] = 7.5x10⁻⁴moles NaOH / 0.205L =

3.66x10⁻³M = [OH⁻]

pOH = 2.44

pH = 14 - pOH

<h3>pH = 11.56</h3>
5 0
2 years ago
You are on an alien planet where the names for substances and the units of measures are very unfamiliar. Nonetheless, you obtain
____ [38]

6.9 Sleps 1. (8)(13) = 15 2. 104/15 = 15/15 3. 6.93333333 4. 6.9 Sleps

6 0
3 years ago
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What mass of hbr (in g) would you need to dissolve a 3.4 −g pure iron bar on a padlock?
vivado [14]

<u>Given:</u>

Mass of pure iron (Fe) = 3.4 g

<u>To determine:</u>

Mass of HBr needed to dissolve the above iron

<u>Explanation:</u>

Reaction between HBr and Fe is

Fe + 2HBr → FeBr₂ + H₂

Based on the reaction stoichiometry-

1 mole of Fe reacts with 2 moles of HBr

# moles of Fe = mass of Fe/atomic mass of Fe = 3.4/56 g.mol⁻¹ = 0.0607 moles

Therefore # moles of HBr = 2*0.0607 = 0.1214 moles

Molar mass of HBr = 81 g/mole

Mass of HBr = 0.1214 moles * 81 g/mole = 9.83 g

Ans: Mass of HBR required is 9.83 g

5 0
3 years ago
Does spring and Fall exist at the poles?
seropon [69]

Answer:

Yes

Explanation:

The tilt of the Earth means the Earth will lean towards the Sun (Summer) or lean away from the Sun (Winter) 6 months later. In between these, Spring and Autumn will occur. The North pole always points the same way as the Earth revolves around the Sun.

4 0
3 years ago
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Help help help ASFAP
gulaghasi [49]

Answer:

A directory of relatives' phone numbers

Hope this helps

Explanation:

5 0
3 years ago
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