The purpose of this experiment is to find the percent composition of each metal in a sample of Scandium and Magnesium alloy, by reacting the alloy sample with hydrochloric acid and collect the hydrogen gas that will evolve over water. Also, to determine the number of moles of hydrogen gas produced by applying the ideal gas law, and measuring the volume, temperature, and the total pressure of the gas using Dalton’s law.

**Introduction: **

Alloys are substances that are composed of more than on element, which at least one of them must be a metal and they have an indefinite proportions. Unlike compounds, in an alloy, the metal is mixed with the other elements but not bonded. In this experiment, a sample of a Scandium and Magnesium alloy is being reacted with a strong acid which is hydrochloric acid producing hydrogen gas. Represented in the following equations:

2*Al* + 6*H* → 2*AL *+ 3*H *

*Zn *+ 2*H *→ *Zn *+ *H*_{2 (}*g*_{)}

The ideal gas law will be used to calculate the number of *H*_{2 (}*g*_{) }moles produced, by first measuring the temperature, total pressure, volume of the gas, and acknowledging the pressure of water vapor. Using the formula;

PV=nRT

And solving for “n” the number of moles of *H*_{2 (}*g*_{) }, where

*n *= __P__*R/ VT*

Also, in order to calculate the pressure of dry *H*_{2 }in mmHg, we need to subtract the total pressure by the vapor pressure of water (mm Hg). The total pressure is found by using Dalton’s

Law, in which the total pressure of the collected gas is equal to the partial pressure of *H*_{2 }

(*g*)

plus the partial pressure of water vapor, plus or minus the water head pressure.

*P **total *= *P **H*_{2}*O *+ *P **H*_{2 }± *P *_{Δ}*H *

A manometer is an instrument used to measure the pressure of a sample gas, in this experiment the concept of a manometer was used when the Δ*H *was calculated by subtracting or adding the water levels in the two bottles based on which one is higher, then subtract that number from the atmospheric pressure to get the pressure of the collected gas.

**Results: **

Data Collected and Calculated From the Three Trials

Trial 1 | Trial 1 | Trial 3 | |

Mass alloy reacted | 1.347 g | 0.318 g | 2.007 g |

Mass Large Bottle filled with water | 4919 g | 3817 g | 4946 g |

Mass Large Bottle after the experiment | 3817 g | 3517 g | 3274 g |

The difference in water heights in bottles | 7.35 cm | 9.94 cm | 2.28 cm |

The temperature of the gas in the bottle | 24.9 °C | 25 °C | 25.2 °C |

The temperature of water in the bottle | 23.2 °C | 24.2 °C | 23 °C |

The volume of water displaced | 1.104 L | 0.301 L | 1.676 L |

Mass Percentage and Standard Deviation of the Elements in the Alloy Sample

Mass percent of Aluminum | Mass percent of Zinc | The standard deviation of % Al | The standard deviation of % Zn | |||

Trial 1 | 42.54 % | 57.46 % | 6.43 % | 6.43 % | ||

Trial 2 | 55.03 % | 44.97 % | ||||

Trial 3 | 42.17 % | 57.83 % |

** **

**Discussion: **

In this experiment, a sample of aluminum-zinc alloy reacted with hydrochloric acid and collected hydrogen gas that got evolved over the water in the bottle, and as much hydrogen gas evolved, water got moved into the other bottle. Also by using the ideal gas law, Dalton’s law, and calculating the volume, temperature, and the total pressure of the gas, helped in determining the number of moles of hydrogen gas and the mass percentage of zinc and aluminum in each sample.

The three alloy samples tested had different masses, in the first trial 1 the alloy sample was 1.347g, the second trial 0.318 g and third trial 2.007 g. And the volume of water displaced increased as the mass of the sample was bigger, where the second trial alloy sample was the smallest and had the lowest volume of water displaced which is 0.301 L, the alloy sample used in the first trial had 1.104 L and the alloy sample used in the third trial was the biggest and had the largest volume of water displaced which is 1.676 L . The first and last trials had close percentages of Zn and Al each compared respectively, in which the first trail had 57.46 % Zn and 42.54 % Al and third trial had 57.83 % Zn and 42.17 %, where the second trial alloy sample had 44.97 % percent of zinc and 55.03 % Aluminum , with the same standard deviation of 6.43 % for both Al and Zn, which is considered not to be very precise.

Also, the temperatures of water and gas in the bottle were similar each respectively, where the temperature of water for the three trials ranged between 23.2 °C to 24.2 °C, and the temperature of the gas in the bottle for the three samples ranged between 24.9 °C to 25.2 °C which is higher than the temperature of water. And the numbers of moles of hydrogen produced in each trial were 0.04254 moles for the first trial, 0.01159 moles for the second trial, and 0.06477 moles for the third trial. As expected the alloy sample with higher mass had more hydrogen gas moles. Furthermore, some sources of error that could affect this experiment can include a leak in the stopper leading to having less hydrogen gas in the bottle, or not leaving the sample to react completely were not all of the hydrogen in the alloy sample is evolved yet.

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

** **

**Conclusion: **

In this experiment, a two-component alloy was analyzed to find the percent of the composition of each element in the sample. By reacting the sample with a strong acid to produce hydrogen gas. This experiment was done by making the sample react in a flask and move the gas to a bottle containing water, where the gas would make the water move to another bottle and take its place. By measuring the difference in the water levels of the bottles, temperature, and pressure using Dalton’s law, the number of moles in each sample can be calculated using the ideal gas law. In which the moles of hydrogen produced is 0.04254 moles for the first trial, 0.01159 moles for the second trial, and 0.06477 moles for the third trial. And the percent of zin in the sample was calculated to be 57.46 % for the first trial, 44.97 % in the second trial, and 57.83 % in the third trial, giving a standard deviation of 6.43 %. The aluminum in the sample had the same standard deviation of 6.43 %, where there was 42.54 % Al in the first trial alloy, 55.03 % in the second trial alloy, and finally 42.17 % Al in the sample of the third trial