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2 years ago

Which of the following is evidence that

Chemistry

1 answer:

tresset_1 [31]2 years ago

4 0

Answer: c. Sugar turning black when it burns.

Explanation:

Chemical change is defined as a change in which rearrangement of atoms take place and leads to formation of new substances.

Physical change is defined as a change which leads to change in shape, size or state of the substance changes. No new substance is formed.

a) Water bubbling when it starts to boil is a physical change as it accompanies only a change in phase.

b) Detergent removing grease from a dish is a physical change as no new substance is formed.

c) Sugar turning black when it burns is a chemical change as there occurs a chemical reaction between sugar and oxygen. The oxygen in the air reacts with the sugar and the chemical bonds are broken.

d) Oil and vinegar separating in salad dressing is not a chemical change. It occurs because of difference in densities.

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what is the approximate ph at the equivalence point of a weak acid-strong base titration if 25 ml of aqueous formic acid require

vivado [14]

Answer:

pH at equivalence point is 8.52

Explanation:

$HCOOH+NaOH\rightarrow HCOO^{-}Na^{+}+H_{2}O$

1 mol of HCOOH reacts with 1 mol of NaOH to produce 1 mol of $HCOO^{-}$

So, moles of NaOH used to reach equivalence point equal to number of moles $HCOO^{-}$ produced at equivalence point.

As density of water is 1g/mL, therefore molarity is equal to molality of an aqueous solution.

So, moles of $HCOO^{-}$ produced = $\frac{29.80\times 0.3567}{1000}moles=0.01063moles$

Total volume of solution at equivalence point = (25+29.80) mL = 54.80 mL

So, at equivalence point concentration of $HCOO^{-}$ = $\frac{0.01063\times 1000}{54.80}M=0.1940M$

At equivalence point, pH depends upon hydrolysis of $HCOO^{-}$ . So, we have to construct an ICE table.

$HCOO^{-}+H_{2}O\rightleftharpoons HCOOH+OH^{-}$

I: 0.1940 0 0

C: -x +x +x

E: 0.1940-x x x

So, $\frac{[HCOOH][OH^{-}]}{[HCOO^{-}]}=K_{b}(HCOO^{-})=\frac{10^{-14}}{Ka(HCOOH)}$

species inside third bracket represent equilibrium concentrations

So, $\frac{x^{2}}{0.1940-x}=5.56\times 10^{-11}$

or, $x^{2}+(5.56\times 10^{-11}\times x)-(1.079\times 10^{-11})=0$

So, $x=\frac{-(5.56\times 10^{-11})+\sqrt{(5.56\times 10^{-11})^{2}+(4\times 1.079\times 10^{-11})}}{2}$

So, $x=3.285\times 10^{-6}M$

So, $pH=14-pOH=14+log[OH^{-}]=14+logx=14+log(3.285\times 10^{-6})=8.52$

5 0

3 years ago

The area in which certain types of plants or animals can be found living in close proximity to each other is called a_________

posledela

I think the answer to this is A

5 0

3 years ago

Read 2 more answers

How many valence electrons would there be for the element with the following orbital diagram?

Svetach [21]

Answer:

Explanation:

The p orbital needs 2 more electrons.

8 0

3 years ago

2) 183 cg = kg 5 .00183 kg 0.0183 kg .183 kg 3) 0.25 kg = g

OlgaM077 [116]

Answer:

183 cg = 0.00183 kg

0.25 kg = 250 g

Explanation:

Use conversion factors. 1kg is equal to 1 x 10^5 cg (100000) and 1 kg is equal to 1 x 10^3 grams (1000 grams).

5 0

3 years ago

In composting, gardeners allow a pile of plant material such as dead leaves to decay. Composting is a form of combustion.

maks197457 [2]

Answer:

This is true

Explanation:

Because it mixes in with the earth making the earth more suitable for gardening and/or farming.

8 0

3 years ago