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11111nata11111 [884]
3 years ago
14

The introduction of synthetic fertilizers and chemical pesticides to farming date back to the __________

Chemistry
1 answer:
laiz [17]3 years ago
4 0

Answer:

Humans started to use pesticides dating back to before 2000 BC.

Hope this helps ^-^

Explanation:

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Chemical digestion would not be possible without _____, which speed up the rate of chemical reactions in your body?
Mashutka [201]
Enzymes in our body increases the speed of chemical digestion.
7 0
3 years ago
Read 2 more answers
Exactly how much time must elapse before 16 grams of potassium-42decays, leaving 2 grams of the original isotope?(1) 8 × 12.4 ho
AleksandrR [38]
The answer is <span>(3) 3 × 12.4 hours
</span>
To calculate this, we will use two equations:
(1/2) ^{n} =x
t_{1/2} = \frac{t}{n}
where:
<span>n - number of half-lives
</span>x - remained amount of the sample, in decimals
<span>t_{1/2} - half-life length
</span>t - total time elapsed.

First, we have to calculate x and n. x is <span>remained amount of the sample, so if at the beginning were 16 grams of potassium-42, and now it remained 2 grams, then x is:
2 grams : x % = 16 grams : 100 %
x = 2 grams </span>× 100 percent ÷ 16 grams
x = 12.5% = 0.125

Thus:
<span>(1/2) ^{n} =x
</span>(0.5) ^{n} =0.125
n*log(0.5)=log(0.125)
n= \frac{log(0.5)}{log(0.125)}
n=3

It is known that the half-life of potassium-42 is 12.36 ≈ 12.4 hours.
Thus:
<span>t_{1/2} = 12.4
</span><span>t_{1/2} *n = t
</span>t= 12.4*3

Therefore, it must elapse 3 × 12.4 hours <span>before 16 grams of potassium-42 decays, leaving 2 grams of the original isotope</span>
7 0
3 years ago
Read 2 more answers
The concentration of protein in a urine sample is calculated to be 2.77 μg/mL. What is the concentration of this solution in uni
maxonik [38]

Answer:

The concentration of this solution in units of pounds per gallon is 2.776*10^{-5} \frac{lb}{gal}

Explanation:

Units of measurement are established models for measuring different quantities. The conversion of units is the transformation of a quantity, expressed in a certain unit of measure, into an equivalent one, which may or may not be of the same system of units.

In this case, the conversion of units is carried out knowing that 1 μg are equal to 2.205*10⁻⁹ Lb and  1 mL equals 0.00022 Gallons. So

2.77 \frac{ug}{mL} = \frac{2.77 ug}{mL}

If 1 μg equals 2.205*10⁻⁹  lb, 2.77 μg how many lb equals?

lb=\frac{2.77ug*2.205*10^{-9}lb }{1ug}

lb=6.10785*10⁻⁹

So, 2.77 μg= 6.10785*10⁻⁹ lb

Then:

2.77 \frac{ug}{mL} = \frac{2.77 ug}{mL}=\frac{6.10785*10^{-9}lb }{mL} =\frac{6.10785*10^{-9}lb }{0.00022 gal} =\frac{6.10785*10^{-9}lb }{0.00022 gal}

You get:

2.77 \frac{ug}{mL} = 2.776*10^{-5} \frac{lb}{gal}

<u><em>The concentration of this solution in units of pounds per gallon is </em></u>2.776*10^{-5} \frac{lb}{gal}<u><em></em></u>

6 0
3 years ago
Maria is baking cookies. She mixes water, flour, sugar, baking powder, butter and chocolate chips and then measures the mass of
Mrrafil [7]

Answer:

The law of conservation of mass was obeyed since some of the mass evaporated while the cookies were baking.

Explanation:

Maria mixes water, flour, sugar, baking powder, butter and chocolate chips and then measures the mass of her ingredients.

Initial mass of ingredients = 1053 g

Final mass = 845 g

All these information are not of any great help.

Law of conservation of mass states that:

For any system closed to all transfers of matter and energy, the mass of the system can not change with respect to time, as system's mass cannot change, any mass can neither be added nor be removed.

In this process of baking, considering the cookies as our system, they never formed a closed system. Hence were free for evaporation.

During the process of baking, water from dough must have evaporated and mass must have reduced.

Hence, the law of conservation of mass was not obeyed.

8 0
3 years ago
Read 2 more answers
Francine makes several measurements of the mass of a metal block. The data set is shown in the table below.
BARSIC [14]

Answer:

Mean

Explanation:

The mean of a series of measurements is calculated when a<em>ll the measurements are added up and then divided by the number of measurements taken</em>, as follows:

  • Sum of Measurements = 20.73 + 20.76 + 20.68 + 20.75 = 82.92

As<u> there are 4 measurements</u>, the mean is:

  • Mean = 82.92 / 4 = 20.73
3 0
2 years ago
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