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Greeley [361]
3 years ago
13

At 25 °C, how many dissociated OH– ions are there in 1243 mL of an aqueous solution whose pH is 2.07?

Chemistry
1 answer:
coldgirl [10]3 years ago
3 0

<u>Answer:</u> The number of OH^- ions dissociated are 8.57\times 10^{11}

<u>Explanation:</u>

We are given:

pH = 2.07

Calculating the value of pOH by using equation, we get:

2.07+pOH=14\\\\pOH=14-2.07=11.93

To calculate hydroxide ion concentration, we use the equation to calculate pOH of the solution, which is:

pOH=-\log[OH^-]

We are given:

pOH = 11.93

Putting values in above equation, we get:

11.93=-\log[OH^-]

[OH^-]=10^{-11.93}=1.17\times 10^{-12}M

To calculate the number of moles for given molarity, we use the equation:

\text{Molarity of the solution}=\frac{\text{Moles of solute}}{\text{Volume of solution (in L)}}

Molarity of solution = 1.17\times 10^{-12}M

Volume of solution = 1243 mL = 1.243 L  (Conversion factor: 1 L = 1000 mL)

Putting values in above equation, we get:

1.17\times 10^{-12}M=\frac{\text{Moles of }OH^-}{1.243L}\\\\\text{Moles of }OH^-=(1.17\times 10^{-12}mol/L\times 1.243L)=1.424\times 10^{-12}mol

According to mole concept:

1 mole of a compound contains 6.022\times 10^{23} number of particles

So, 1.424\times 10^{-12}mol number of OH^- will contain = (1.424\times 10^{-12}\times 6.022\times 10^{23})=8.57\times 10^{11} number of ions

Hence, the number of OH^- ions dissociated are 8.57\times 10^{11}

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Answer:

  • <em>Hydration number:</em> 4

Explanation:

<u>1) Mass of water in the hydrated compound</u>

Mass of water = Mass of the hydrated sample - mass of the dehydrated compound

Mass of water = 30.7 g - 22.9 g = 7.8 g

<u>2) Number of moles of water</u>

  • Number of moles = mass in grams / molar mass

  • molar mass of H₂O = 2×1.008 g/mol + 15.999 g*mol = 18.015 g/mol

  • Number of moles of H₂O = 7.9 g / 18.015 g/mol = 0.439 mol

<u>3) Number of moles of Strontium nitrate dehydrated, Sr (NO₃)₂</u>

  • The mass of strontium nitrate dehydrated is the constant mass obtained after heating = 22.9 g

  • Molar mass of Sr (NO₃)₂ :  211.63 g/mol (you can obtain it from a internet or calculate using the atomic masses of each element from a periodic table).

  • Number of moles of Sr (NO₃)₂ = 22.9 g / 211.63 g/mol =  0.108 mol

<u>4) Ratio</u>

  • 0.439 mol H₂O / 0.108 mol Sr(NO₃)₂ ≈  4 mol H₂O : 1 mol Sr (NO₃)₂

Which means that the hydration number is 4.

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                     Gold is one of the most precious metal metal used in many applications and mainly as a jewellery. In terms of purity it is categorized in Karats. 24 Karat is considered the purest Gold (i.e. 100 % Gold) while other Karats (14, 18, 22 e.t.c) are alloys with other metals and gyms.

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