A 120.5 g sample of water loses -7525 J of energy. What was the

In a five-fold serial dilution of a 20 ug/mL solution, all tube dilutions are 1/5. What is the substance concentration in the th

sergij07 [2.7K]

Answer:

In the third tube, the concentration is 0.16 ug/mL

Explanation:

In the first step, the solution is diluted by 5. Then, the concentration will be

20 ug/mL / 5 = 4 ug/mL

Then, in the second step this 4 ug / ml solution is diluted by a factor of five again:

4 ug /ml / 5 = 0.8 ug/mL

This solution is then diluted again by 5 and the concentration in the third tube will be then:

0.8 ug/mL / 5 = 0.16 ug/mL

Another way to calculate this is to divide the original concentration by the dilution factor ( 5 in this case) elevated to the number of dilutions. In this case:

Concentration in the third tube = 20 ug/mL / 5³ = 0.16 ug/mL

3 0

3 years ago

Read that From picture and tell me the answer please

Dafna11 [192]

Answer:

1g Hydrogen

Explanation:

<h3>Getting to the equation:</h3>

Calcium in water reacts vigorously to give a cloudy white Precipitate (compound) called Calcium hydroxide alongwith the evolution of Hydrogen gas.

$\boxed{ \mathsf{Ca + H_2O \rightarrow Ca(OH)_2 + H_2}}$

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

<h3>Balancing the equation: </h3>

This reaction is not in it's balanced form! The number of atoms of Hydrogen on the left is 2 while that on the right is 4,I.e.,they're not equal.

Adding a 2 in front of H2O solves the problem by making the number of atoms of each element on both the sides equal.

$\mathsf{Ca +2 H_2O \rightarrow Ca(OH)_2 + H_2}$

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

<h3>Observations:</h3>

Looking into the equation more carefully, we see:

1 atom of Calcium reacts with 2 molecules of water to give 1 molecule of Calcium Hydroxide alongwith 1 molecule of Hydrogen gas.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

<h3>Gram atomic and molecular masses </h3>

Mass of one atom of Calcium = it's gram atomic mass

= 40 g

Mass of one "molecule" of Hydrogen

= it's Gram molecular mass

= gram mass of one atom × number of atoms in one molecule

= 1 × 2

= 2 g

So,

according to our observation:

One atoms of Calcium gives one molecule of Hydrogen (during the particular reaction)

=> 40g of Calcium gives = 2g of Hydrogen

•°• 1 g of Calcium gives = $\frac{2}{40}$

= $\frac{1}{20}$ g Hydrogen

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

<h3>Answer:</h3>

We're provided with 20g of Calcium,

=> 20g of Calcium gives = 20 × $\frac{1}{20}$ g H2

= 1 g H2

_______________

Hope this helps!

6 0

3 years ago

I really need help with this.

suter [353]

The answer to question 8 is
Ethanol's Molar Heat of Combustion. ... Heats of combustion are quoted as positive numbers while the enthalpy changes of combustion reactions (ΔH) are quoted as negative numbers, as combustion reactions are always exothermic. Heats of combustion are typically stated in kilojoules per mole (kJ/mol. or kJ mol. -1).
can u mark me the brainliest

7 0

3 years ago

Two liters of a perfect gas are at 0>c and 1 atm. if the gas is nitrogen, n2, determine the number of molecules.

ZanzabumX [31]

Solution;

The gas is at STP;

Where; T = 273 K , P = 1 atm

We know that 1 mole of a gas at STP occupies a volume of 22.4 liters .

V1/n1 = V2/n2

n2 = (V2/V1) n1

n2 = (2 l/22.4 l)(1 mole)

n2 = 0.0893 moles

But 1 mole of a compound has 6.022 × 10^23 molecules

Thus, number of molecules = 0.0893 moles × 6.022 ×10^23 molecules

= 5.378 × 10^22 molecules.

4 0

4 years ago

X³-216? can someone help me with this prob?

andre [41]

Cube root the -216 which will make x = cubedroot(-216) or x = -6

4 0

4 years ago