All Chemistry Questions & Answers

Which reference electrode to select for electrochemical measurements? The one with Vycor or ceramic frit?
Is there any significant difference in quality and accuracy between reference electrode with Vycor frit (porous glass attached with heat-shrink tube) and the one 
equipped with ceramic frit (molten in the glass tube) like in this example
Percentage By Mass Calculation

A 4.675g sample of limestone (impure CaCO3) was treated with 375ml of 0.261 molL^-1 hydrochloric acid. After the reaction was over, the mixture was filtered and a 25 ml sample of the filtrate required 17.62ml of 0.0517 molL^-1 barium hydroxide solution for complete neutralisation. 

How do I find the initial energy of an electron given the wavelength and the final energy An electron jumps to the n = 4 level of a hydrogen atom after absorbing a photon of wavelength 1875 nm. What energy level did the electron move from? I haven't found equations for how to to find the energy absourbtion, just emission.
What is the percentage of cocaine in the mixture?

A sample of cocaine, C17H21O4N, is diluted with sugar, C12H22O11. When a 1.00 mg sample of this mixture is burned, 2.00 mg CO2 is formed. What is the percentage in this mixture?

Can someone please explain and show me how to di this question please....

Jacy bought a gold necklace weighing 21.3 grams from the flea market. She filled a graduated cylinder with water to the 5.0mL mark and dropped her necklace in. The level in the  graduated cylinder rose to 704mL. is her necklace real or fake?

chem question

could you please help me with this question:

how many grams of water must be added to 200 ml of NaOH solution in order to have a solution with a specific gravity of 1.157, 13.55%? (Specific gravity= 1.32, 28.83%).

How to convert wt% MgCO3 to mole% MgCO3

I have geochemistry data for limestone samples consists of oxides and REE. I want to find out the mole% MgCO3 for the samples. I understand that I can use conversion factor of 3.4683 to convert MgO wt% to MgCO3 wt%. But from there I don't know how to proceed.

Is this the correct oxidation numbers for H and O in hydrogen peroxide H2O2; H 1+, O 1- . Why or why not ?

Yes H is +1 and O is -1 is peroxides so these oxidation numbers are correct .

What is the oxidation number of nitrogen in nitric acid,HNO3 ?

Nitrogen has +5 oxidation number in HNO3

Is the reaction 2Al(s) + 3Cl 2 (g) ----> 2AlCl 3 (s) can be considered as the redox reaction ?

Yes, since Al is underging an oxidation and Cl is undergoing reduction .