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3 years ago

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Carbon -11 is a radioactive isotope of carbon. It’s half life is 20 minutes. What amount of the initial mass of 70.0g of C -11 a

toms in a sample will be left after 80 minutes

1 answer:

dusya [7]3 years ago

6 0

Answer:

4.38g

Explanation:

70.0/2 = 35g - 20 mins

35/2 = 17.5g - 40 mins

17.5/2 = 8.75g - 60 mins

8.75/2 = 4.375g - 80 mins

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What amount of heat is released when the temperature of 450.0 g of a

Molodets [167]

Answer:

$\boxed {\boxed {\sf 4038.48 \ Joules}}$

Explanation:

Since we are given the mass, specific heat, and change in temperature, we should use this formula for heat:

$q=mc\Delta T$

The substance's mass is 450.0 grams, the specific heat is 1.264 J/g°C, and the change in temperature is 7.1 °C.

$m= 450.0 \ g \\c= 1.264 \ J/g \textdegree C\\\Delta T= 7.1 \ \textdegree C$

Substitute the values into the formula.

$q= (450.0 \ g)(1.264 \ J/g \textdegree C)(7.1 \ \textdegree C)$

Multiply the first 2 values together. The grams will cancel out.

$q= 568.8 \ J/ \textdegree C (7.1 \ \textdegree C)$

Multiply again. This time, the degrees Celsius cancel out.

$q= 4038.48 \ J$

<u>4038.48 Joules</u> of heat energy are released.

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A chemical element is a pure substance that consists entirely of what?

Novosadov [1.4K]

Ans: consists of atoms

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The model below shows a part of a human body's muscular system.

Ann [662]

Answer:

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Explanation:

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What is Climate Change and how can it effect plants?

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Climate change will make plants—and us—thirstier. The combined effects of increased CO2 levels and warmer temperatures will increase water consumption by vegetation. That will lead to water declines in streams and rivers like the Ashepoo River in South Carolina

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Calculate the ph at the equivalence point for the titration of 0.230 m methylamine (ch3nh2) with 0.230 m hcl. the kb of methylam

Vlad1618 [11]

Answer: The pH at the equivalence point for the titration will be 0.65.

Solution:

Let the concentration of $[OH^-]$ be x

Initial concentration of $[CH3NH_2]$ , c = 0.230 M

$CH_3NH_2+H_2O\rightleftharpoons CH_3NH_3^++OH^-$

at eq'm c-x x x

Expression of $K_b$ :

$K_b=\frac{[CH_3NH_3^+][+OH^-]}{[CH_3NH_2]}=\frac{x\times x}{c-x}=\frac{x^2}{c-x}$

Since ,methyl-amine is a weak base,c>>x so $c-x\approx c$ .

$K_b=\frac{x^2}{c}=5.0\times 10^{-4}=\frac{x^2}{0.230 M}$

Solving for x, we get:

$x=1.07\times 10^{-2} M$

Given, HCl with 0.230 M , it dissociates fully in water which means $[H^+]$ = 0.230 M

$[OH^-]=[H^+]$ will result in neutral solution, since $[OH^-]$

Remaining $[H^+]$ after neutralizing $[OH^-]$ ions

$[H^+]_{\text{left in solution}}=[H^+]-[OH^-]=0.230-1.07\times 10^{-2}=0.2193 M$

$pH=-log{[H^+]_{\text{left in solution}}=-log(0.2193)=0.65$

The pH at the equivalence point for the titration will be 0.65.

8 0

3 years ago