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Elis [28]
3 years ago
6

Why is a control needed in a valid experiment?

Chemistry
1 answer:
aliina [53]3 years ago
5 0
You need a control so you have something to compare the experimental group on-- If you don't have a control group, how will you know what's changed?
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What mass of aluminum is needed to produce 0.500 mole of aluminum chloride?
3241004551 [841]

Answer:  " 13.5 g Al " ;

                    →  that is:  "13.5 grams of aluminum."

<u>____________________________</u>

Explanation:

<u>____________________________</u>

<u>Note</u>: What is missing from the question is the "balanced chemical equation" for the "chemical reaction" that contains:

 The reactants:  "aluminum (Al) " ;  and "chlorine (Cl) " ;  and:

 The product:    "aluminum choloride (AlCl₃) " .

____________________________

The "balanced chemical equation" is:

____________________________

        2 Al   +   3 Cl₂   →   2 AlCl₃   ;

_____________________________

<u>Note</u>: The molecular weight of "aluminum (Al)" is:   " 26.98 g /mol " .

____________________________

So:  We call solve using a technique known as:  "dimensional analysis" :

____________________________

  0.500 mol AlCl₃ * (\frac{2mol Al}{2mol AlCl_{3} }) * (\frac{26.98g Al}{1 mol Al}) = ?

____________________________

<u>Note</u>:  The units of "mol AlCl₃" cancel out to "1' ; and:

          The  units of "mol Al" cancel out to "1" ; and we are left with:

____________________________

 " \frac{(0.500 * 2 * 26.98)}{2}   g Al ["grams of aluminum"] ;

____________________________

<u>Note</u>: We can "cancel out the "2's" ; since "2/2 = 1 " ; and we have:

 →  (0.500 * 26.98) g Al ;

    = 13.49 g Al ;

         →  Round to 3 (Three) significant figures;

         →  Since:  "0.500" has 3 (Three) significant figures:

____________________________

   =  13.5 g Al ; that is:  "13.5 grams of aluminum."

____________________________

 Hope this is helpful!  

      Best wishes to you in your academic pursuits—and within the "Brainly" community!

____________________________

3 0
3 years ago
The atomic mass of oxygen is 15.999 amu whatbdoes the value equal
sweet-ann [11.9K]

Answer:

The sum of the protons and neutrons.

Explanation:

protons + neutrons = atomic mass

7 0
3 years ago
Why is it important for the pH of blood to remain constant
fenix001 [56]
<span>Blood pH has an ideal level of about 7.3 to 7.4. It is important for the pH ofblood to remain constant because if your blood pH varies, itcan be deadly.<span>hope this helps </span></span>
7 0
3 years ago
determine the frequency and wavelength (in nm) of the light emitted when the e- fell from n=4 and n=2
Lostsunrise [7]

Answer:

Frequency = 6.16 ×10¹⁴ Hz

λ = 4.87×10² nm

Explanation:

In case of hydrogen atom energy associated with nth state is,

En =  -13.6/n²

For n = 2

E₂ = -13.6 / 2²

E₂ = -13.6/4

E₂ = -3.4 ev

Kinetic energy of electron = -E₂ = 3.4 ev

For n = 4

E₄ = -13.6 / 4²

E₄ = -13.6/16

E₄ = -0.85 ev

Kinetic energy of electron = -E₄ = 0.85 ev

Wavelength of radiation emitted:

E = hc/λ = E₄ - E₂

hc/λ = E₄ - E₂

by putting values,

6.63×10⁻³⁴Js × 3×10⁸m/s / λ = -0.85ev   - (-3.4ev )

6.63×10⁻³⁴ Js× 3×10⁸m/s / λ = 2.55 ev

λ = 6.63×10⁻³⁴ Js× 3×10⁸m/s  /2.55ev

λ = 6.63×10⁻³⁴ Js× 3×10⁸m/s  /2.55× 1.6×10⁻¹⁹ J

λ = 19.89 ×10⁻²⁶ Jm / 2.55× 1.6×10⁻¹⁹ J

λ = 19.89 ×10⁻²⁶ Jm / 4.08×10⁻¹⁹ J

λ = 4.87×10⁻⁷ m

m to nm:

4.87×10⁻⁷ m ×10⁹nm/1 m

4.87×10² nm

Frequency:

Frequency = speed of electron / wavelength

by putting values,

Frequency = 3×10⁸m/s /4.87×10⁻⁷ m

Frequency = 6.16 ×10¹⁴ s⁻¹

s⁻¹ = Hz

Frequency = 6.16 ×10¹⁴ Hz

3 0
3 years ago
A compound is formed when 171.2 g of carbon reacts with 28.8 g of hydrogen. What is the mass percent of hydrogen in the compound
IgorLugansk [536]
Following the law of conservation of mass, the mass percent of hydrogen in the resulting compound is 14.4%(wt/wt). This is assuming that all of the carbon reacts with all of the hydrogen. The solution is as follows:

mass % = mass hydrogen*100/total mass = 28.8*100/(28.8+171.2) = 14.4%
4 0
3 years ago
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