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abruzzese [7]
4 years ago
8

The half-life of radioactive element krypton-91 is 10 seconds. if 16 grams of krypton-91 are initially present, how many grams a

re present after 10 seconds? after 50 seconds?
Chemistry
1 answer:
earnstyle [38]4 years ago
6 0
10 seconds = 8grams
then just divide by 2 another 4 times...
 = 0.5grams after 50 seconds
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What is the ph of 0.450 m al(no3)3 [ka for al3+(aq) = 1.00x10-5]? express your answer to two decimal places?
White raven [17]

Answer : The pH of the solution is, 2.67

Explanation :

The equilibrium chemical reaction is:

                           Al^{3+}+H_2O\rightarrow Al(OH)^{2+}+H^+

Initial conc.       0.450                   0               0

At eqm.           (0.450-x)                 x               x

As we are given:

K_a=1.00\times 10^{-5}

The expression for equilibrium constant is:

K_a=\frac{(x)\times (x)}{(0.450-x)}

Now put all the given values in this expression, we get:

1.00\times 10^{-5}=\frac{(x)\times (x)}{(0.450-x)}

x=0.00212M

The concentration of H^+ = x = 0.00212 M

Now we have to calculate the pH of solution.

pH=-\log [H^+]

pH=-\log (0.00212)

pH=2.67

Therefore, the pH of the solution is, 2.67

8 0
3 years ago
The mass of an electron is 9.11× 10–31 kg. What is the uncertainty in the position of an electron moving at 2.00 × 106 m/s with
Kruka [31]
Just use the Heisenberg Uncertainty principle: 

<span>ΔpΔx = h/2*pi </span>

<span>Δp = the uncertainty in momentum </span>
<span>Δx = the uncertainty in position </span>
<span>h = 6.626e-34 J s (plank's constant) </span>

<span>Hint: </span>

<span>to calculate Δp use the fact that the uncertainty in the momentum is 1% (0.01) so that </span>

<span>Δp = mv*(0.01) </span>

<span>m = mass of electron </span>
<span>v = velocity of electron </span>

<span>Solve for Δx </span>

<span>Δx = h/(2*pi*Δp) </span>

<span>And that is the uncertainty in position. </span>
6 0
3 years ago
How many grams of h2 will be produced if 175g of HCI are allowed to react completely with sodium
Sedbober [7]

Answer:

4.8 grams of H₂ will be produced if 175g of HCI are allowed to react completely with sodium

Explanation:

By stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction) you can see that the following amounts in moles of each compound react and are produced:

  • HCl: 2 moles
  • Na: 1 mole
  • NaCl: 2 moles
  • H₂: 1 mole

You know the following masses of each element:

  • H: 1 g/mole
  • Cl: 35.45 g/mole
  • Na: 23 g/mole

So, the molar mass of each compound participating in the reaction is:

  • HCl: 1 g/mole + 35.45 g/mole= 36.45 g/mole
  • Na: 23 g/mole
  • NaCl: 23 g/mole + 35.45 g/mole= 58.45 g/mole
  • H₂: 2* 1 g/mole= 2 g/mole

Then, by stoichiometry of the reaction, the following amounts in grams of each of the compounds participating in the reaction react and are produced:

  • HCl: 2 moles* 36.45 g/mole= 72.9 g
  • Na: 1 mole* 23 g/mole= 23 g
  • NaCl: 2 moles* 58.45 g/mole= 116.9 g
  • H₂: 1 mole* 2 g/mole= 2 g

So, a rule of three applies as follows: if by stoichiometry, when reacting 72.9 grams of HCl 2 grams of H₂ are formed, when reacting 175 grams of HCl how much mass of H₂ will be formed?

mass of H_{2} =\frac{175 g of HCl*2g ofH_{2} }{72.9 g of HCl}

mass of H₂= 4.8 g

<u><em>4.8 grams of H₂ will be produced if 175g of HCI are allowed to react completely with sodium</em></u>

3 0
3 years ago
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quester [9]
Is there an attachment because it depends on the element.
5 0
3 years ago
To which of the third period element does this belong
Mrac [35]

Explanation:

A period 3 element is one of the chemical elements in the third row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when the periodic table skips a row and a chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon. The first two, sodium and magnesium, are members of the s-block of the periodic table, while the others are members of the p-block. All of the period 3 elements occur in nature and have at least one stable isotope.[1]

7 0
3 years ago
Read 2 more answers
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