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2 years ago

URGENT ! PLEASE ANSWER QUICKLY

Chemistry

2 answers:

Bumek [7]2 years ago

7 0

Answer:If we dissolve NaF in water, we get the following equilibrium:

text{F}^-(aq)+text{H}_2text{O}(l) rightleftarrows text{HF}(aq)+text{OH}^-(aq)

The pH of the resulting solution can be determined if the K_b of the fluoride ion is known.

20.0 g of sodium fluoride is dissolve in enough water to make 500.0 mL of solution. Calculate the pH of the solution. The K_b of the fluoride ion is 1.4 × 10 −11 .

Step 1: List the known values and plan the problem.

Known

mass NaF = 20.0 g

molar mass NaF = 41.99 g/mol

volume solution = 0.500 L

K_b of F – = 1.4 × 10 −11

Unknown

pH of solution = ?

The molarity of the F − solution can be calculated from the mass, molar mass, and solution volume. Since NaF completely dissociates, the molarity of the NaF is equal to the molarity of the F − ion. An ICE Table (below) can be used to calculate the concentration of OH − produced and then the pH of the solution.

Explanation:

marysya [2.9K]2 years ago

4 0

Answer:

not sure if this is 100% correct but this is what i got first question: molarity=mol/L 5g*1mol/58.44g=5/58.44 =0.085558mol 4.8m=0.085558/L L=0.0178

jiujuan avatar

second question: pH = - log [H3O+] pH= -log [4.6*10^-9] = 8.33724216

Explanation:

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The earth has enough gravity to do that

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What mass of carbon monooxide must be burned to produce 175 kJ of heat under standard state condaitions?

Sphinxa [80]

Answer:

17.3124 grams

Explanation:

Given;

Amount of heat to be produced = 175 kJ

Molar mass of the carbon monoxide = 12 + 16 = 28 grams

Now,

The standard molar enthalpy of carbon monoxide = 283 kJ/mol

Thus,

To produce 175 kJ heat, number of moles of CO required will be

= Amount heat to be produced / standard molar enthalpy of CO

= 175 / 283

= 0.6183

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number of moles = Mass / Molar mass

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0.6183 = Mass / 28

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2 years ago

What is the solution to the problem rounded to the correct number of significant figures? 8.01 × 4.1 = ? A. 32.8 B. 32.84 C. 32.

kicyunya [14]

<u>Answer:</u> The correct option is Option D.

<u>Explanation:</u>

Significant figures are defined as the figures that represent the digits of a number which carry an important contribution to the numerical value, starting with the first non-zero digit. For Example: 105.268 has 6 significant figures because every digit carry its own contribution towards the numerical value.

Whenever there is multiplication, the answer will contain the same number of significant figures as there are in the least precise numerical value.

Significant figures in 8.01 are 3 and that in 4.1 are 2.

So, the answer of these two numerical value will contain 2 significant figures.

$8.01\times 4.1=32.841\approx 33$

Hence, the correct option is Option D.

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2 years ago

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A sheet of polyethylene 1.5-mm thick is being used as an oxygen barrier at a temperature of 600K. If the flux is 2.48 x 10-5 kg/

Eddi Din [679]

Complete Question

The complete question is shown on the first uploaded image

Answer:

The concentration of high-pressure side is $C_1 = 0.722 \ kg/m^3$

Explanation:

From the question we are told that

The thickness of the polyethylene is $d = 1.5 \ mm = 0.0015 \ m$

The temperature is $T = 600 \ K$

The flux is $JA = 2.48 *10^{-5} \ kg/m^2\cdot s$

The concentration on the low-pressure side is $C_2 = 0.5 \ kg/m^3$

The initial diffusivity is $D_o = 6.2 *10^{-4} \ m^2 /s$

The activation energy for diffusion is $Q_d = 41 \ kJ /mol = 41*10^3 J /mol$

Generally the diffusivity of the oxygen at 600 K can be mathematically evaluated as

$D = D_o * e^{- \frac{Q_d}{R * T } }$

substituting values

$D = 6.2*10^{-4} * e^{- \frac{41 *10^3}{8.314 * 600 } }$

$D = 1.671 *10^{-7} \ m^2 /s$

Generally the flux is mathematically represented as

$JA = D * \frac{C_1 -C_2}{d}$

Where $C_1$ is the concentration of oxygen at the higher side

$C_1 = d * \frac{JA}{D} + C_2$

substituting values

$C_1 = 0.0015 * \frac{2.48*10^{-5}}{1.671*10^{-7}} + 0.5$

$C_1 = 0.722 \ kg/m^3$

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zavuch27 [327]

Answer:

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Explanation:

Good Luck!

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