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frosja888 [35]
2 years ago
11

Cell membranes are selectively permeable. This means that A. only water can move freely across the cell membrane. B. any substan

ce can move across the cell membrane, but chemical energy will always be required. C. some substances can move freely across the cell membrane, while others must be transported. D. no substances can move freely across the cell membrane.
Chemistry
1 answer:
MaRussiya [10]2 years ago
6 0

Answer:

C. some substances can move freely across the cell membrane, while others must be transported.

Explanation:

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If the K a Ka of a monoprotic weak acid is 7.3 × 10 − 6 , 7.3×10−6, what is the pH pH of a 0.40 M 0.40 M solution of this acid?
olga_2 [115]

Answer:

pH =3.8

Explanation:

Lets call the monoprotic weak acid HA, the dissociation equilibria in water will be:

HA + H₂O   ⇄ H₃O⁺ + A⁻    with  Ka = [ H₃O⁺] x [A⁻]/ [HA]

The pH is the negative log of the H₃O⁺ concentration, we know the equilibrium constant, Ka and the original acid concentration. So we will need to find the [H₃O⁺] to solve this question.

In order to do that lets set up the ICE table helper which accounts for the species at equilibrium:

                          HA                                   H₃O⁺                          A⁻          

Initial, M             0.40                                   0                              0

Change , M          -x                                     +x                            +x

Equilibrium, M    0.40 - x                              x                               x

Lets express these concentrations in terms of the equilibrium constant:

Ka = x² / (0.40 - x )

Now the equilibrium constant is so small ( very little dissociation of HA ) that is safe to approximate 0.40 - x to 0.40,

7.3 x 10⁻⁶ = x² / 0.40  ⇒ x = √( 7.3 x 10⁻⁶ x 0.40 ) = 1.71 x 10⁻³

[H₃O⁺] = 1.71 x 10⁻³

Indeed 1.71 x 10⁻³ is small compared to 0.40 (0.4 %). To be a good approximation our value should be less or equal to 5 %.

pH = - log ( 1.71 x 10⁻³ ) = 3.8

Note: when the aprroximation is greater than 5 % we will need to solve the resulting quadratic equation.

4 0
3 years ago
1. A 5.04 mL sample of Cu has a mass of 45 grams. What is the density of Cu? Show units in final answer
babunello [35]
I think the answer is number D…. I think
4 0
2 years ago
Which of the following environmental risks is most likely to lead to digestive health issues?
algol13


Meat contamination because humans do not eat air or fertilizer so meat contamination is the only logical answer.


6 0
3 years ago
Read 2 more answers
In the metric system kilo is an abbreviation for 10,000
SCORPION-xisa [38]

Answer:

10 kilo

Explanation:

5 0
2 years ago
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For the following reaction, 33.7 grams of bromine are allowed to react with 13.0 grams of chlorine gas.
Ira Lisetskai [31]

Explanation:

The reaction is given as;

Br2(g) + Cl2(g) ----> 2BrCl(g)

From the equation;

1 mol of Br2 reacts with 1 mol of Cl2

Converting the masses given to moles, using the formular;

Number of moles = Mass / Molar mass

Br2;

Number of moles = 33.7 g / 159.808 g/mol = 0.21088 mol

Cl2;

Number of moles = 13.0 g / 70.906 g/mol = 0.18334 mol

From the values;

0.18334 mol of Cl2 would react with 0.18334 mol of Br2 with an excess of 0.02754 mol of Br2

<em>What is the maximum amount of bromine monochloride that can be formed? __________grams</em>

<em />

1 mol of Cl2 produces 2 mol of Bromine Monochloride

0.18334 mol of Cl2 would produce x

Solving for x;

x = 0.18334 * 2 = 0.36668 mol

Converting to mass;

Mass = Number of moles * Molar mass = 0.36668 mol * 115.357 g/mol

Mass = 42.299 g

<em />

<em>What is the FORMULA for the limiting reagent?</em>

<em />

The limiting reagent is Cl2 as it determines the amount of product formed. The moment the reaction uses up Cl2, the reaction stops.

<em>What amount of the excess reagent remains after the reaction is complete? __________grams</em>

The excess reagent is Br2

The number of moles left is;

0.02754 mol of Br2

Converting to mass;

Mass = Number of moles * Molar mass = 0.02754 mol  * 159.808 g/mol

Mass = 4.401 g

7 0
2 years ago
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