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Anna007 [38]
3 years ago
13

A compound is known to be Na2CO3, Na2SO4, NaOH, NaCl, NaC2H3O2, or NaNO3. When a barium nitrate solution is added to a solution

containing the unknown a white precipitate forms. No precipitate is observed when a magnesium nitrate solution is added to a solution containing the unknown. What is the identity of the unknown compound
Chemistry
1 answer:
Westkost [7]3 years ago
6 0

Answer:

Na₂SO₄

Explanation:

Barium nitrate, Ba(NO₃)₂ produce precipitate with SO₄²⁻, CO₃²⁻. That means the precipitate could be obtained from Na₂SO₄ and Na₂CO₃.

Also, magnesium nitrate, Mg(NO₃)₂, produce precipitate just with CO₃²⁻. As the unknown solution produce no precipitate, the unknown compound is:

<em>Na₂SO₄</em>

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A 10.0-ml sample of 0.200 m hydrocyanic acid (hcn) is titrated with 0.0998 m naoh. what is the ph at the equivalence point? for
ryzh [129]
When the titration of HCN with NaOH is:

HCN (aq) + OH- (aq) → CN-(aq) + H2O(l)

So we can see that the molar ratio between HCN: OH-: CN- is 1:1 :1

we need to get number of mmol of HCN = molarity * volume 

                      = 0.2 mmol / mL* 10 mL = 2 mmol

so the number of mmol of NaOH = 2 mmol according to the molar ratio

so, the volume of NaOH = moles/molarity

                                          = 2 mmol / 0.0998mL

                                          = 20 mL

and according to the molar ratio so, moles of CN- = 2 mmol

∴the molarity of CN- =  moles / total volume 

                                   = 2 mmol / (10mL + 20mL ) = 0.0662 M

when we have the value of PKa = 9.31 and we need to get Pkb

so, Pkb= 14 - Pka

            = 14 - 9.31 = 4.69 

when Pkb = -㏒Kb

         4.69 = -㏒ Kb 

∴ Kb = 2 x 10^-5

and when the dissociation reaction of CN- is:

CN-(aq) + H2O(l) ↔ HCN(aq) + OH- (aq) 

by using the ICE table:

∴ the initials concentration are:

[CN-] = 0.0662 M

and [HCN] = [OH]- = 0 M

and the equilibrium concentrations are:

[CN-] = (0.0662- X)

[HCN] = [OH-]= X

when Kb expression = [HCN][OH-] /[CN-]

by substitution:

2 x 10^-5 = X^2 / (0.0662 - X)

X = 0.00114 

∴[OH-] = X = 0.00114

when POH = -㏒[OH]

                    = -㏒ 0.00114

POH = 2.94

∴PH = 14 - 2.94 = 11.06



 

7 0
3 years ago
2 2. The energy stored in a substance that can be released when the substance reacts. A. Mechanical Energy B. Thermal Energy C.
vichka [17]

Answer:

C. Chemical Energy

Explanation:

The energy that stored in the substance or in compounds is called chemical energy which released when the substance reacts.

A substance is made up of atoms and molecules and chemical energy is present in those atoms or molecules. When a chemical reaction takes place, these energy released from atoms and molecules.

Chemical energy can be released in the form of  thermal energy (heat) and mechanical energy (working ability).

Hence, the correct answer is "C. Chemical Energy".

4 0
3 years ago
(4.2 x 10^8) + (2.6 x 10^6) *
hodyreva [135]

Answer:

4.226×10^8

Explanation:

4.2 ×10^8+2.6×10^6=422600000

or 4.226×10^8

5 0
3 years ago
What is the correct answer and why?
MariettaO [177]
A) number of neutrons in the nucleus... all isotopes of an element contain the same number of protons which is equal to that elements atomic number...
hope this helps!
7 0
3 years ago
The vapor pressure of pure ethanol at 60 °c is 0.459 atm. raoult's law predicts that asolution prepared by dissolving 10.0 mmol
Vlad1618 [11]
Raoult's law is stated as<span> the partial </span>vapor pressure<span> of each component in the </span> mixture<span> of ideal liquids is equal to the vapor pressure of the pure component multiplied by its </span>mole fraction<span> in the mixture. Mathematically, it is expressed as

P = Xi Pi

where P= vapor  pressure of solution
Xi = mole fraction of i component
Pi = vapor pressure of pure i component.

In present case, P1 = 0.459 atm and n1 = number of mole  of ethanol = 0.090
n2 = number of mole of </span><span> naphthalene = 0.01

</span>∴ Mole fraction of ethanol = \frac{n1}{\text{n1 + n2}} = \frac{0.090}{\text{0.090 + 0.010}}  = 0.9

Thus, vapor pressure of solution = 0.9 X 0.459 = 0.4131 atm. 

Answer: <span>The vapor pressure of pure ethanol at 60 °c is 0.459 atm. Raoult's law predicts that a solution prepared by dissolving 10.0 mmol naphthalene (nonvolatile) in 90.0 mmol ethanol will have a vapor pressure of 0.4131 atm.</span>
6 0
3 years ago
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