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2 years ago

Which of the following is the best definition of a physical change?

Chemistry

2 answers:

Eddi Din [679]2 years ago

8 0

You’re best choice is B

ELEN [110]2 years ago

7 0

I think answer is

C. Something that can be observed or measured while changing the identity of the substance

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A 0.15 m solution of chloroacetic acid has a ph of 1.86. What is the value of ka for this acid?

dem82 [27]

Answer: $1.67\times 10^{-3}$

Explanation:

$ClCH_2COOH\rightarrow ClCH_2COO^-+H^+$

cM 0 0

$c-c\alpha$ $c\alpha$ $c\alpha$

So dissociation constant will be:

$K_a=\frac{(c\alpha)^{2}}{c-c\alpha}$

Given: c = 0.15 M

pH = 1.86

$K_a$ = ?

Putting in the values we get:

Also $pH=-log[H^+]$

$1.86=-log[H^+]$

$[H^+]=0.01$

$[H^+]=c\times \alpha$

$0.01=0.15\times \alpha$

$\alpha=0.06$

As $[H^+]=[ClCH_2COO^-]=0.01$

$K_a=\frac{(0.01)^2}{(0.15-0.15\times 0.06)}$

$K_a=1.67\times 10^{-3]$

Thus the vale of $K_a$ for the acid is $1.67\times 10^{-3}$

4 0

3 years ago

If the half-life of a radioisotope is 10,000 years, the amount remaining after 20,000 years is

Cloud [144]

Answer:

Considering the half-life of 10,000 years, after 20,000 years we will have a fourth of the remaining amount.

Explanation:

The half-time is the time a radioisotope takes to decay and lose half of its mass. Therefore, we can make the following scheme to know the amount remaining after a period of time:

Time_________________ Amount

t=0_____________________x

t=10,000 years____________x/2

t=20,000 years___________x/4

During the first 10,000 years the radioisotope lost half of its mass. After 10,000 years more (which means 2 half-lives), the remaining amount also lost half of its mass. Therefore, after 20,000 years, the we will have a fourth of the initial amount.

6 0

3 years ago

How did the Bohr model of the atom affect scientific thought?

Vadim26 [7]

Answer:

C. Scientists accepted the model at first but later rejected it.

Explanation:

Scientists accepted the model at first because it explained the hydrogen emission spectrum.

However, with the development of quantum mechanics, scientists had to modify the model (not reject it).

Electrons still had specific energies, but they no longer travelled in fixed orbits.

Instead, electrons had a probability of being found in a given region of space.

5 0

3 years ago

Read 2 more answers

Mercury can be obtained by reacting mercury(I) sulfide with calcium oxide. How many grams of calcium oxide are needed to produce

OLga [1]

First, 55 g of Hg is 3.65 moles because one mole of Hg has a molar mass of 200.59

Then, the mole ratio of Hg to CaO is 8:4 or 2:1. SO we divide 3.65 by 2 to get 1.82 moles of CaO

This is the same as 102.06 grams because one mole of CaO has a molar mass of 56.0774

Hope this helps!

4 0

3 years ago

Mercury has a density of 13.6 g/mL. How many milliliters of mercury have a mass of 350 g? *

Colt1911 [192]

solution:

density x volume=mass volume x volume

13.6gml x 3.55ml

thus,the object has a mass of 98.3g

7 0

3 years ago